Danish director and co-founder of the Dogme '95 Brotherhood, Lars von Trier, is no stranger to controversy. His 1996 Breaking the Waves met with wide international acclaim but also had a fair share of very vocal detractors. His contribution to the Dogme movement, the extraordinary but confrontational Idioterne [The Idiots], was far more divisive: during the ovation following its screening at Cannes, critic Mark Kermode was ejected for disrupting the proceedings by repeatedly shouting "Il est merde!" ("It's shit!").

In the wake of this, von Trier made no attempt to play safe and Dancer in the Dark polarised opinion even more dramatically than his previous features. The movie's web site actually traded on this, placing positive and negative quotes alongside one another and urging people to go see it and make up their own minds, sound advice for any film, no matter what any idiot with a DVD player and a word processor (myself included) might say. Perhaps the biggest surprise to some of us was that, despite his dislike of the director's previous work, Mark Kermode admitted to being rather impressed by it.

The story elements will be familiar to anyone with a passing knowledge of musical melodrama. Selma is a Czech immigrant who has come to America to chase a dream. Unbeknown to those around her, she is going blind, a congenital disease that she knows her son will eventually fall victim to without corrective surgery, something she works long hours in a factory job in the hope of paying for. A lover of musicals, she sometimes escapes her daily drudgery by imagining she is starring in a musical of her own, creating an idealised reality in which she can sing, dance and see, where the problems of the real world simply have no meaning. But just as she is close to saving the amount required for the operation, events take a dark and eventually tragic turn.

Dancer in the Dark is both a musical and an anti-musical, placing standard genre plot developments in a realistic setting and effectively nullifying the studied artificiality that makes even the most dramatic turns in most musicals a 'safe' emotional experience. Couple this with the Dogme-like, aggressively hand-held camerawork and jump-cut editing and the result is startling: with the emotional safety barrier provided by the genre's stylistic characterisations and settings removed, seemingly familiar scenes, characters and plot twists carry an emotional wallop that leaves you reeling. When characters suffer here, it hurts. Kicking against traditional mainstream narrative, Dancer never lets the audience off the hook, taking them on a journey that at times is genuinely punishing, but for me it was more emotionally involving and genuinely upsetting than anything else I saw that year. Lest we forget, von Trier is not the first to travel this road – in the late 70s, Dennis Potter took a very similar slant on the musical with his brilliant TV series Pennies From Heaven, whose final act clearly prefigures that of Dancer. But even Potter gave the audience a last-minute (if fanciful) get-out – it's clear well before the end of Dancer that von Trier is going to do no such thing.

The musical numbers also kick against the norm. Written by Icelandic composer and singer Björk, the music veers more towards the avante-garde than the sweep and rhythm of Irving Berlin or Rogers and Hammerstein, but is dreamily seductive nonetheless. These sequences differ stylistically from the main body of the film in that they were shot using what Trier has dubbed the 100 camera unit, an ambitiously experimental technique in which 100 high-end domestic DV cameras were placed in key positions all around the location, then the musical numbers performed in one continuous take, as they would be on stage. This results in some unusual camera angles and atypical editing, which focusses less on the dance moves than on creating a seemingly random filmic rhythm, and just occasionally produces moments of real inspiration that could not have been feasibly achieved using traditional techniques.

If this realistic approach is to work then the performances also need to kick against the stylistic genre norm. Much would clearly be required of the lead, so there was considerable skepticism when it was announced that Björk would be taking the role. But for those of us who groan at the whole concept of singers who really want to be actors, her performance here is an absolute revelation – she does not simply play the role, she becomes it, immersing herself so completely that the line between performer and character vanishes completely (the commentary tracks confirm the extent to which this is true). The demands made on her in the second half of the film, and especially the final twenty minutes, would tax even the most experienced actors, by Björk never falters for a second, and her very real terror towards the end is utterly heartbreaking, reducing many of those at our cinema screening to tears, myself included.

But Björk is not the only one who delivers here – every part is played in convincingly naturalistic fashion, some winningly so. To bag a star of Catherine Deneuve's status in a supporting role is something of a coup, but to have her come across as a completely convincing woman-next-door is a real achievement. She and Björk play off each other wonderfully, really selling the idea that they've been good friends for some time and making for most believable shop floor workers. Peter Storemare creates an engagingly sad figure in Jeff, a man who loves Selma but is unable to adequately articulate his feelings, and David Morse, one of the few American actors in the film, does a sterling job as Selma's friend and landlord, a policeman whose slavery to his wife's spending drives him to betray everything he supposedly stands for.

Dancer in the Dark is both a heart-rending drama and a deconstruction of the Hollywood musical, reconstituted into something new and remarkable. Von Trier enriches the experience through layering and subtext, commenting on issues such as poverty, the plight of migrant workers, the American legal system, capital punishment and the pressures of consumerism without ever allowing them to dominate the drama – all are integral aspects of the story and how the characters move through it. Opinion may remain violently divided, but I sit absolutely with von Trier on this one. For me, he has created an astonishing, intelligent and innovative musical drama that manages to be so much more than this simple description suggests. It seems so right that this film won both the Palme D'Or and the Best Actress award at Cannes – this is cinema at its most genuine, and most emotionally affecting.

Both the region 1 and region 2 disks are presented in anamorphic widescreen, the region 2 being 2.35:1 and the region 1 2.40:1, a difference barely noticeable on-screen. Be aware of one thing straight up, Dancer in the Dark was shot on video rather than film, and though professional equipment was used for the main storyline, the dance numbers were captured on cameras just one step away from the ones you'll find down at Dixons. This considered, the transfer on both disks is impressive. Detail and black levels are strong, and the film rarely betrays is video origins (compared to, say, Series 7: The Contenders, whose TV news look was part of its aesthetic), and colours, though deliberately muted, are faithfully reproduced. Pixelation is almost never evident. There is a very clear shift of picture quality and style during the musical sequences, but this was deliberate, a combination of shooting on lower quality mini-DV camcorders and post-production treatment of the video to enhance the colouration and give the sequences a more vibrant look that clearly separates them from the rest of the film.

Here the disks differ, the region 2 having a 5.1 sound mix while New Line's disk has a DTS track. In truth there is little to choose between them, in part because the film uses digital sound in such an unusual and effective way. The main story, Selma's real world, is monaural, confined almost exclusively to the centre speaker; it is only during the musical sequences that the full sound stage kicks in, and most effectively so, filling the room with song and putting us inside Selma's world and imagination. This provides an aural differentiation between her two worlds that matches the visual shift mentioned above. Lower frequencies are minimal, but during the 107 Steps song they contribute well to an already dark and affecting sequence. Some have complained at the lack of surround effects outside of the music numbers, but I think this approach works exceptionally well and is totally in-keeping with von Trier's almost experimental approach to the whole project. 5.1 and 2.0 soundtracks are also offered on the region 1 disk. The 2.0 is adequate, but does not have the spread or depth of the other tracks during the musical numbers.

It's here that the real difference between the two disks lies. On the surface, VCI's region 2 disk appears to do rather well on extras, but on the whole they are much thinner than the list on the menu might suggest.

First up is the almost inevitable Theatrical Trailer, which is anamorphic 2.35:1 and Dolby 2.0 and in good shape (unlike the cropped 4:3 debacle on Film Four's Straight Story disk).

A Behind the Scenes featurette is non-anamorphic 16:9 and shows von Trier working with the actors, which is indeed fascinating stuff, but at just over 4 minutes in length it is way too short and ends before it's really got going. Von Trier provides some information in the shape of interview and voice-over, in Danish, with English subtitles, but this is half-hearted even for a featurette.

Slightly more substantial at 10 minutes is an Interview with von Trier, which is again 16:9 non-anamorphic but conducted in English. Though in a relaxed posture, he doesn't seem totally at ease with the interview process and is less forthcoming and chatty than he appeared in documentaries like The Name of This Film is Dogme 95, but does supply some interesting information about his thinking on the film. One of my favourite bits has him say of Björk's music, "I like the music very much. Some of it I had to learn to like."

Cannes 2000 is the most threadbare and frankly superficial extra of all and consists of a single, 1 minute 11 second shot of von Trier and his leading players walking down the steps at the Cannes film festival. Surely there must have been more footage to use than that – the film won the Palm D'Or and Best Actress!

Finally we have Selma's Songs, allowing you to go straight to any of the songs in the film, something a good chapter selection menu would also enable you to do.

New Line's Platinum Series disk is a special edition and justifies that status, with a much more substantial set of extras.

There are two featurettes, located in a Documentaries sub-menu in the Special Features. 100 Cameras: Capturing Lars von Trier's Vision is a 14 minute look at the 100 camera unit used for the musical sequences. This includes interviews with von Trier, choreographer Vincent Paterson, and Peter Hjorth, the unit's technical supervisor, plus footage of the unit installing the cameras and the control system, known as Sonja. Shot on 16:9 anamorphic DV, image quality is variable – while outside footage looks good, some of the interviews and interior footage are a little grubby, but the content is always worthwhile.

Even more fascinating is Choreography: Creating Vincent Paterson's Dance Sequences, which is technically similar to the 100 Camera featurette and features an interview with Paterson, plus a great deal of his own DV footage of the rehearsal process, including work with Björk and his own coverage of the 100 camera unit shoots. Running at 24 minutes this is an enlightening and constantly interesting extra, giving a very useful glimpse of the rehearsal process, and how the numbers look when the visual dazzle of the 100 camera unit is removed.

Alternate Scenes presents alternative cuts of the Cvalda musical number and two alternative cuts of I've Seen it All. Cvalda is presented in anamorphic 2.35:1 but appears to have been transferred from what looks like a low grade video master, and is well short of the main feature in quality. It is nevertheless useful stuff, as it appears to be the cut originally assembled by Vincent Paterson and referred to in his commentary track. The two cuts of I've Seen It All are presented 16:9 anamorphic, though appear to have been squashed up a bit from a 2.35:1 original. They are still interesting, as the cut is very different in both and gives a flavour of the freedom the 100 camera unit can give you on the editing bench.

Selma's Music is exactly the same as the Selma's Songs extra on the region 2 disk, taking you directly to the film's musical numbers, while Cast and Crew gives film listings for the main cast and von Trier, but no detailed biographies to accompany them.

Without doubt the best feature are the two screen-specific Commentary Tracks. The first features director Lars von Trier, producer Vibeke Windelov, technical supervisor Peter Hjorth and artist Per Kirkeby. Kirkeby's contribution is exclusive to the opening overture, for which he did the paintings, and gives useful information about the process of creating the artwork and the thinking behind it. Hjorth's sections are brief and deal exclusively with the technical issues surrounding the 100 camera unit, which while interesting enough has been lifted in its entirety from the 100 Cameras featurette, and if you've already watched that then nothing here will be new. Vibeke Windelov gives a lot of background detail into the film's production, including communication problems that developed between Björk and von Trier, though never explains exactly how this situation came to be. At one point the commentary track actually stops to make way for an audio recording of von Trier directing the scene playing out on screen, giving an idea of just how he works with actors on set.

But it's von Trier himself who is the prize here. This is his first and to date only commentary track (at least in English), and as previous interviews and documentaries (specifically on the Dogme 95 movement) have demonstrated, he is an interesting and intelligent speaker. Here he provides a lot of information on the production and the thinking behind it, the casting process and the development of the characters, and how his own social and political convictions shaped key scenes. Despite his considerable achievement, he thankfully avoids the sort of back-slapping self-congratulation that makes many commentary tracks on disks of recent US movies so wearing, and freely admits that at times he made wrong decisions, one of which may have contributed to the eventual communication problems with his star. There are also a few surprises – I, for one, was genuinely startled to learn that the twitchy, hand-held camerawork and jump-cut editing style was primarily influenced not by the experiments with the Dogme movement, but by the superb US TV series, Homicide: Life on the Street.

But there's more. A Second Commentary Track is also provided by choreographer Vincent Paterson. I approached this one with some trepidation, figuring it would be largely silent and only come to life during the musical numbers, when it would deal exclusively with the technical aspects of the dance steps. How wrong I was. Not only is Paterson a great talker, but was involved with the production from an early stage and had key duties on the 100 camera unit. He also quickly became the main liaison between Björk and von Trier, especially when communication difficulties set in. As such he was present for the entire shoot and contributes a great deal of information on a wide variety of aspects of the production. This is a consistently fascinating track, and compliments the main track perfectly.

Dancer in the Dark is always going to have its detractors, especially those for whom mainstream cinema is king, an attitude this film kicks resolutely against. This is challenging cinema, stylistically and thematically, and that alone makes it worth a look, but von Trier's direction, coupled with Björk's stunning central performance, elevate it to essential cinema – confrontational, experimental, and emotionally devastating.

As for which disk to go for, that will depend on what you're looking for. For picture and sound quality the Film Four region 2 delivers, but if you want more than just the film itself and thrive on extras then the New Line disk is a must – the featurettes are informative and the two commentary tracks are of a very high standard.