I've heard it suggested that the greatest get-out clause in modern cinema is the caption that opens the first Star Wars film – "A long time ago in a galaxy far away" establishes not only that the worlds depicted within the film are not directly related to our own, but that these events happened not in some version of our future, but in someone else's past. With that simple statement George Lucas told his audience that in this world anything goes, and if the fashions look dated, if a laser pistol looks like a WW2 Mauser, then that's because the universe in which this film takes place developed along different lines to our own, and that any such similarities are thus purely coincidental. But running a close second to this must be "Based on a true story", where "based on" allows the filmmaker to get creative with (a cynical view might be "trade on the notoriety of") a real-life character or event and fictionalise aspects of both whilst presenting them as fact. The extent to which this is seen as a good or bad thing depends in part on the degree to which events and characters are drawn from reality: no-one really had issues with the fact that Tobe Hooper's The Texas Chain Saw Massacre bore an only passing resemblance to the activities of Ed Gein, but Oliver Stone has been repeatedly ticked off for juggling with the facts in movies such as JFK and Nixon.

Based as it is on the life of multiple-murderer Aileen Wuornos, or at least a small part of it, Monster carries the aforementioned disclaimer, but ultimately sets itself up as a true catalogue of the events that ultimately led to the arrest and execution of a woman who was incorrectly dubbed "America's first female serial killer." Although the names of all of the characters except Wuornos have been changed, presumably because the people in question are all still alive (as far as the movie world is concerned, you're fair game once you're dead), many of the principal figures are drawn from real life and the event timeline is, for the most part, fairly accurate. But debut writer-director Patty Jenkins, having apparently researched her movie thoroughly, still plays fairly loose with the truth, and having adopted a specific viewpoint for her story, she massages the facts through alteration and omission to avoid contradicting it. The result is a film that is at times impressive in its recreation of recorded events, and at others misleading, romanticised, and frankly a little cheesy.

The story of Aileen Wuornos is a complex one. To this day, much of it remains the subject of speculation, and whether she killed in self-defence or cold blood has never been definitively confirmed. Wuornos always maintained that she was brutally raped by her first victim, Richard Mallory (credence was later given to this when it was revealed that Mallory had previously spent five years in jail for violent rape in another state, but no retrial was granted on the basis of this new evidence) and that her other victims had either attacked or attempted to assault her and that she was acting purely in self defence. Towards the end of her twelve years on death row she unexpectedly changed her plea, claiming that she had killed them for their money only. But in their compelling documentary, Aileen: Life and Death of a Serial Killer, filmmakers Nick Broomfield and Joan Churchill cast considerable doubt on this, the suspicion being that she had altered her story in order to speed up her execution as she was no longer able to cope with her death row existence.

It is these killings and Aileen's relationship with her lover Tyria Moore (here renamed Selby) that form the crux of a film that has all the ingredients of a standard teenage drama. A wrong 'un with a dark past meets the right girl and, despite the disapproval of the girl's guardians, the two run off together. The relationship changes both of their lives, but the past eventually catches up with them with tragic results, testing their love and ultimately destroying them. Of course the difference here is that both of the characters are women, and it is to the film's considerable credit that it presents their relationship as a natural and loving one, the problems that arise having nothing to do with gender or sexual preference. But even at this early stage the film has started to stray. The use of Aileen's POV voice-over heavily romanticises her grim childhood and her early days as a call girl – she was chasing a dream, the film suggests, and was getting in cars with men not to make money after she was thrown out of home (living in the woods as she was, if a punter took her to a motel for sex, it would offer her the chance to wash and warm herself), but because she believed that any one of them might be movie producer who would 'discover' her and make her into a star. This also suggests a desire to be famous at all costs, a low-key speculation thrown in to the mix of Why Aileen Killed.

Cut (in a smartly executed edit) to Aileen sitting beneath an underpass contemplating suicide, and one last drink lands her by chance in a gay bar and introduces her to Selby, whose attempted pick-up she angrily rejects, telling her in no uncertain terms that she is not of that persuasion. The movie chooses to use this awakening of her until-then undiscovered lesbianism as a turning point for Aileen, whereas in truth this was not her first gay relationship and it seems likely that she knew full well she was entering a gay bar, probably in search of the very companionship she found. What is not in dispute is the importance of the relationship with Tyria/Selby to Aileen – in a life that was characterised by abuse and exploitation, this was the only true love she ever knew.

It's the presentation of Selby that best illustrates the film's schizophrenic attitude to the facts of the case. It's deemed OK to present Wuornos as she was, a woman of earthy appearance whose tough life is reflected in her looks and her attitude, in part because her case is so well documented and her face so widely known. She's also presented as an essentially masculine figure, where the values of aggression and toughness are more important than beauty, something symbolically represented by the replacement of the real-world Wuornos's .22 pistol with a .44 Magnum, the gun of choice for Dirty Harry and a favourite example of a firearm as an all-destroying phallus. But we're still in an American movie with an audience demographic in mind, so to balance this we have Christina Ricci's wide-eyed cuteness as Selby, a woman just about anyone can appreciate the appeal of (well, not the regulars in the gay bar, it seems) and a far cry from the hardened features of the woman on whom she is based. You can't help but imagine the discussion – "Goddamn it, we have to sell this – at least one of the lead characters has to be pretty!"

The first murder extends this fact/fiction approach. With no hard evidence as to exactly what took place save for the number of shots fired, the conversation and activity during all of the depicted killings are a matter of speculation. Yet for the encounter with the Richard Mallory stand-in, writer-director Jenkins has chosen to take Wuornos's account pretty much at her word (though aggressive invasion by a foreign object has replaced rape, something that actually comes across as nastier) and presents Wuornos very much as the victim and her attacker's death as a cathartic necessity. The film also uses this assault and its aftermath to both complicate and propel forward the still undeveloped relationship between Wuornos and Selby, whereas in truth Wuornos and Moore had been together for three years when this incident occured. This proves something of a blueprint for the rest of the film, with fact and fiction blended for dramatic effect, sometimes to the detriment of the story being told, as the truth, though more complicated and with fewer straightforward answers, is often more interesting than the over-familiar relationship clichés that are sometimes employed in its name.

Though his earlier rape conviction has leant credence to Wuornos's account of Mallory's supposed assault, the other six killings have remained a subject for sometimes wild theorising, from the Freudian (she was killing her father over and over again), to the stupidly sensationalist (she was a lesbian man-hater), to Wuornos's own claim that she was acting in self-defence and her later assertion that it was all a matter of robbery and eliminating witnesses. Monster seems keen to flirt with several of these theories, and following the self-defence plea of the first attack, Wournos is transformed into an avenging angel of the Christian moral right (oxymoron time again), killing a punter after he requests she call him daddy while they do the deed and prompting her to spit "fucking child molester!" after she has shot him, trading on what has of late become a tiresomely lazy way of labeling someone as deserving all they get. All of the early encounters present Wuornos as the innocent and her punters as sleazy, abusive scumbags, which has the effect of shaping Aileen into a female Travis Bickle, the real rain that has come to wash the scum off the streets. A particularly fanciful sequence in which she tries for a secretarial job and is soundly humiliated by another pompously judgemental male ensures that we know she tried everything in her power to avoid this life direction, and the seedy cop who drives her to a garage and demands a blow-job confirms that the police will offer no help to someone like her. To hammer the point home, Wuornos is subjected to further humiliation by the cop in question, and it's revealed that when he arrested her on a previous occasion he almost broke her skull. In this world, all men really are scum.

As money becomes tight and Selby pressures Aileen to return to prostitution, the prinicipal motivation for the killings switches to robbery tinged with a dose of man-hating, with the moralistic undertone still ever-present (before killing a man who turns out to be an ex-cop, Wuornos sneers at his unfaithful attitude to his wife, then tells him how much she loathes men). This is emphasised by the pick-up she lectures about his desire to play it rough as a prelude to killing him, only to have him whimper that he's not like that and has never done this before. He escapes with his life and a quick hand-job, which Wuornos administers with a look of barely controlled revulsion. The final killing, in which a man who was simply offering to help Wuornos pleads for his life and is shot to cries of "I'm sorry!" suggests that it was here that Wuornos unwittingly crossed the line. Of course, now that she's killed someone that the film has marked as undeserving, it's finally time for the police to wake up and catch her. This presents us with a rather tabloid view of the whole situation, reviving memories of the so-called Yorkshire Ripper, Peter Sutcliffe, who did not become a subject of outrage for the British press until he killed his first non-prostitute.

As events come to a head and the police start to close in, the film is back on more solidly factual ground, though remains dramatically shakey. Wuornos's eventual arrest is even filmed in the actual biker bar in which it took place, though this cuts little ice given the games played with the truth elsewhere. The decision not to even mention the short but non-violent relationship Wuornos had with Dick Mills after Tyria had left her may have been made for dramatic flow, but it also serves to re-enforce the presentation of Aileen as a woman who, with the exception of Bruce Dern's easy-going old (and non-sexual) sage, only ever received abuse from the men she encountered, never kindness or even tolerance. If truth and legend collide, print the legend.

The final courtroom scenes are handled in ultra-brief style, but even then we are carefully steered to see Aileen as a tragic anti-hero. Her defiant, angry response to her verdict – "May you rot in hell! Sending a raped woman to death!" – is close to the what she actually said. Yet by omitting her furiously hateful "I hope your wife and kids get raped – right in the ass!" the film avoids any willful nastiness on Aileen's part and gets to keep her as a victim, having been betrayed by the woman she loved and sentenced to death by an uncaring (male) judge who is uninterested in her claims that she was trying to defend herself. All of which is true, from a certain perspective, but a look at the documentary footage of this event shows just how sanitised and unambiguous the film has become by this stage.

Though ultimately even a film that is based on fact must stand and fall by its effectiveness as a drama, it is its very relation to the real Wuornos case and the news footage, interview material and documentaries surrounding it, that serves to illustrate both the film's strengths and its weaknesses. Central to this is Charlize Theron's performance as Wuornos. A traditional Hollywood beauty, she has transformed herself here both facially and physically (teaming her with the diminutive Ricci emphasises her height, another male characteristic), and she has clearly studied footage of Wuornos in full vitriolic flow. As an impersonation it is sometimes uncannily accurate, but despite the widespread acclaim and the Academy Award, there is a nagging sense that the entire performance was based on footage of Wuornos after she had spent twelve years on death row, when so long spent in isolation had turned the calm, communicative and lucid talker seen in Nick Broomfield's 1992 Aileen Wuornos: The Selling of a Serial Killer into a sometimes wild-eyed woman on the edge of insanity whose mood could change in a second. Theron plays her this way for much of the film, volatile, extremely unstable, and almost always a couple of twitchy steps away from violence. It's a showy and at times fascinating portrayal, but is also disappointingly restrictive. Comparisons with the documentary footage of the real-life Wuornos serve to highlight both the impressive accuracy of aspects of Theron's performance and the fact that the Wuornos herself actually had a greater range, so to speak.

There is an unfussy efficiency to much of the film that serves the storytelling well, but this is repeatedly undermined by moments of quite horrible Hollywood clunkiness, almost always surrounding the relationship between Aileen and Selby. Music is the chief offender here, and is often either poorly used or just plain annoying. This is first evident in the rather twee musical accompaniment to Aileen and Selby's first, largely innocence night together, but really makes its mark at a skating rink as the pair venture out together and finally kiss, and a horribly cheesy pop song is cranked up in an explosion of Hollywood romantic mawkishness. The scene is clearly designed to show Wuornos as a woman of love, passion and commitment, but it's so crassly handled that I, for one, was having trouble holding down my lunch. Later, as Aileen emerges from the bathroom ready to really commit to their relationship, another ghastly pop singer warbles loudly, "I don't really know her....but I think I could love her...." and on Aileen's proclamation of love to Selby, the warbler pipes up with "What a beautiful feeling..." followed by some nightmarish guitar twanging that had me scrabbling for the volume control. Though things never get this bad again, this state-the-bleedin'-obvious use of music pops up several times, notably when Wuornos is cutting out newspaper clippings of her crimes (very serial killer) and her relationship with Selby is straining, and the radio blurts out: "I'm gonna keep on lovin' you.....'cause it's the only thing I wanna do..." There is also a tendency to build to key events – one of the shootings, the verdict at her trial – with an onslaught of electronic guitar twanging that rises to a crescendo and seems to shout "HERE COMES A BIG MOMENT!" at you in an extraordinarily unsubtle way.

As we get closer to the end, the film slips more and more into familiar troubled relationship territory, and Wuornos's tearful emotional collapse at the bus station comes across as an uncomfortable mix of tragedy, guilt and over-the-top histrionics. By then, this complicated true-life story has been reduced to the level of B-movie melodrama, which has prompted more than one reviewer to note the similarity of this film's style and approach to that of the exploitation features of Roger Corman. Viewed on that level, Monster certainly has a lot going for it – as it never flags, creates an effective anti-hero (in part by making almost everyone else seem worse), and is energetically performed. But there is a sense that with a little less reliance on twee romanticism, storytelling cliché, over-simplification and drama-inspired fact-bending, this could have been much more powerful and affecting work.

Framed at 1.85:1 and anamorphically enhanced, the transfer is, for the large part very pleasing – colour and contrast are impressive throughout, and sharpness is generally good, if a tad soft in a couple of places. There is some artefacting in areas of similar colour such as the gay bar where Aileen and Selby meet – the background shimmers quite a bit here. On the whole, though, night-time scenes are very well rendered and daylight shots are very good.

Both a 5.1 and a DTS track have been included, the main difference between them being one of volume. The surrounds are reasonably well used, though more for music and atmospheric sound effects than specifically directed sounds (a lot of musical elements seem to end up at the back). Surprisingly little use seems to be made of the subwoofer, but on the whole this is a pleasing enough, if unadventurous mix.

You can pretty much discount the three trailers that precede the film as true extras – they are there to sell other Columbia Tristar titles and cannot be skipped, but pressing the menu button on your remote should sort that.

The Making of Monster featurette is 4:3 and stereo and is effectively a 15 minute EPK. There is plenty of talk of the film's intention to get deeper than any other look at the Wuornos story, plus a good deal of the sort of back-slapping and self-congratulation that we have come to expect from these electronic press kits. It also touches on Theron's make-up, and the fact that some of the film was shot on the locations at which the real events took place. Image quality here is somewhat variable, especially the film extracts.

Theatrical Trailer runs for just over 2 minutes, is non-anamorphic 1.85:1 and stereo and gives a reasonable flavour of the film, including that music.

The International Trailer is also non-anamorphic 1.85:1 and stereo and actually sells the film more effectively by making the love story element seem less tacky. It runs for 2 minutes 20 seconds.

Monster "Surrounded" is a 30 second promo for the soundtrack album, something I personally will not by buying.

Film Mixing Demo is a moderately interesting extra that allows you to play a 2 minute sequence from the film with just the dialogue, music of effects tracks, or combinations of them.

Interview with Patty Jenkins and BT or, as it announces itself when the film starts, Monster – Evolution of the Score is a 15 minute featurette presented in anamorphic 16:9 and, astonishingly, DTS (there is also a 2 channel soundtrack), though this is for the music rather than the interview material, which is underscored by some very audible tape hiss in places. The content has director Patty Jenkins and composer of the film's music, known as BT, discussing the score and the unusually wide 5.1 spread of the mix. Once again, there is a fair amount of back-slapping, but also a reasonable attempt to explain how the score came technically and artistically together. Of course, as someone who found the score seriously irritating, this was not an extra that thrilled me, but if you do like the music then this is definitely for you, though Jenkins' very American over-enthusiasm can grate a bit.

The Aileen Wuornos story is by turns fascinating, sad and disturbing, and is way too complex for any single film to do full justice to. Monster has been widely hailed for its central performance, its authenticity, and its feeling for the character of Wuornos herself. Despite its very real virtues, I remain largely unconvinced. For me, Monster feels like an old-style exploitation movie in the ill-fitting coat of serious drama, one that sometimes visibly strains at the seams. Efficient rather than inspired, and featuring a central performance that is both impressive and a little narrow in scope, it too often lets serious drama slip into the realms of romantic cliché, something the music score seems almost designed to hammer home. This aside, there is a fascinating irony in the fact that Theron won her Oscar for playing Wuornos on 29th February, that leap year day that only occurs once every four years and, yes, the real-life Aileen's birthday. And despite my own issues with the film, part of me can't help thinking that Aileen herself would have rather liked it.

This disc itself is a reasonable package, a decent transfer, a DTS soundtrack and a couple of OK extras. Fans of the film may well mourn the lack of a commentary track, but Jenkins' over-enthusiasm in the extra features leaves me happy enough with the decision. Definitely take a look at Monster, but then see the Nick Broomfield documentary double on Wuornos, which for my money are more gripping, more disturbing, and oddly enough, more emotionally affecting.