You have prejudices. No, really, you do. So have I. We couldn't live any other way. Of course, the less eye-catching way of saying the same thing is that we have choices and we have to make choices every minute of our lives, sometimes not based on previous experience. The only exception is when our subconscious makes choices for us and we call that dreaming. Let's not beat around the South African bush. Note, I said prejudices, not quite the same thing as racism. Why? Because who wants a flaming storm of hate saline slow-dripped into their digital veins at even the shadow of a misunderstanding? Racism is bad news any way you slice it. Judging someone positively or negatively based on what bit of the planet their mothers wetly ejected them on to – or their skin shade – or religious affiliation – is frankly profound ignorance cloaking a brain sadly untouched by the burden of common sense.

Anyone can be decent and anyone can be a bastard. Most of us are constantly changing mixtures of both with a lion's share of the former or we'd all be at each other's throats most of the time. But we are human and our base instinct is to find those we want to be with (when it comes to family, we have no choice) and protect those relationships thereby logically keeping a great many people away or 'the others' as we may know them. We do like our 'other' to be readily recognised. So what if we found the best example of 'other' a human being could possibly find? How about scuttling, tentacled extraterrestrials? Yup, they'll do.

An alien mothership settled over Johannesburg over twenty five years ago. Mankind eventually found inside its cargo of extraterrestrial refugees, worker drones, and resettled them on Earth at District 9, a ghetto by any other name. Complete with flourishing human crime-lords, violence bubbling away under the surface, an alien taste for cat food and a number of weapons no human can operate, District 9 is a powder keg. Along comes multi-national man Wikus with a match and a smile. He's here to evict the 'prawns' as we delightfully refer to the ETs. I'll admit that when I heard about District 9 and its premise of unwanted, unloved 'immigrant' aliens living in shanty towns in Jo'berg, I was non-plussed by the unsubtle anvil-heavy metaphor that seemed to be at the heart of the enterprise. But it seems that Blomkamp has fashioned his science fiction action picture in a society in which he has had experience by simply growing up there.

If segregation and apartheid was the norm in society to a growing lad, why not impose the ultimate 'others' in a similar predicament and see how that plays out. Not well? Yeah… Not well at all. A good friend of mine once said that he could judge the goodness in someone seeing how well or badly they treated their inferiors (by this he meant pets not fellow human beings). Boy, he'd have had a hard time with District 9. The one thing Blomkamp has succeeded in doing with a fair amount of panache is to make the audience forget about the obvious politics lurking and punching out from beneath the squalor. His movie does one thing that is not welcome but didn't detract too much from the enjoyment of the results of his canny craft and talent. District 9 consistently reminds the audience that when human beings disengage, they can exhibit behavioural atrocities that leave you breathless with rage or shame. Our 'hero' – if he ever gets to earn that status – is a bureaucratic speciesist who regards the extraterrestrials as little more than animated fodder to be sacrificed for order and slaughtered on a whim, a whim that comes from the profoundly seated hatred of the 'other'. He torches nascent aliens and enjoys communicating their death throe whelps with a smile and a knowing Quiz Show host air. This makes you want to head butt the guy into the middle of next week. I was seriously wishing disaster on this man from twenty minutes in. And lo and behold, my wishes were granted. Ain't movie retribution grand?

OK, easing up a little, Wikus is a seriously twisted soul nominally put in charge of the eviction squad because he happens to be married to his boss's daughter. He reminded me of Michael Palin's Jack, the hero's torturer in Gilliam's Brazil. He has that same ostensible likeability which is undercut by darker aspects of his character you hope never to encounter in reality. Wikus is doing his job in the full knowledge that he's going to be making millions of lives (alien, but still lives) less well off, incite riots in which both alien and human will inevitably die and – as he gets his way – if he finds alien young, he burns them alive. I've never seen such a convincing smile on an actor for quite a while, that sincere, folksy grin that makes you complicit in his nastiness. He's smiling at you because he assumes with all the arrogance of deeply ingrained racism, that you're agreeing with his own point of view. It's a genuinely heartfelt and creepy performance not made any better by its locale. The word comeuppance doesn't take long to form in the mind. And it takes even less time to be visited upon this hideous, grinning monster.

Let's not rain on anyone's parade here and state categorically that Blomkamp is a talented director at home with both film-making and digital effects (he did those astonishing Citröen commercials with the ice-skating 'transformer' cars). His association with 'Lord of the Everythings'', Peter Jackson, can only be a big plus creativity and career wise. For a modest budget he has made a film that crucially delivers on many fronts. We care, we are excited, we are fleetingly aware of the subtext (ho ho) and most of all, we leave the cinema with word of mouth desperate to be memed to others. It's just that humanity comes off as irredeemably awful and I know we are just that, collectively, but sometimes in cinemas you can find a glimmer of hope. Just sometimes you can convince yourself that we're not all power mad, racist thugs with the empathy of a dull blade. Sometimes you can find a Hotel Rwanda.

The plot point of the alien weapons is the real MacGuffin and it had me stumped. Why did the aliens not simply use the weapons? It was also suggested that the aliens are not the brightest bunch though one was clearly bright enough to engineer a way out of their predicament. Only later did I gather up a mostly 'post deleted' series of posts on the IMDB from someone, shall we say, unhappy with the movie. They flagged the alien character/ intelligence issue with the modernity and scope of the weaponry as something that made no sense. With a little bit of imagination, you could concur that like Douglas Adams' telephone sanitizers and hair dressers (the middle people on the B Ark from the 2nd radio series of Hitchhiker's Guide), these aliens were the lowest on the totem pole and that the technology came from their higher thinkers who'd sent them to Earth to get rid of them? Am I going too far into this?

Much has been said about the revolutionary way Blomkamp tells his story. Uh… OK. It's not so much revolutionary as an entwining of every means available to record visual information. It has vox pops, news, hand-cam POV, corporate style, kinetic documentary, 2008/09 'standard' movie making (the latter of which edges everything else out as the story reaches its climax save the odd 'news' helicopter shot). The marriage of all these formats is nicely judged in terms of pace and you never feel like the gimmick is overdone or less effective than a straight forward shoot. I'm not sure just how much more effective the film would have been or not been as a standard shoot. Yes, there is some pleasure from seeing something presented as 'real' but hasn't that technique become almost a cliché by now? Or does it still bring audiences into the action in ways we have been conditioned to be led via the ubiquity of visual information? There's an academic paper in there somewhere.

So where does this leave Wikus? Well, he's exposed to alien gloop and starts to mutate into one of them in a very Brundlefly sort of way as bits of him start falling off. I thought fondly of The Quatermass Experiement as it's his arm that changes first. Of course, this inconvenience changes Wikus's world. On trumped up 'having sex with alien' Photoshopped charges, he is ostracised and hunted down by those who wish to exploit his new found gift of being able to fire alien weaponry. But even the most hardened bastard would start to see things differently if you wake up one morning and in the mirror you are staring at what you despised yesterday. So starts Wikus's heroic rise to the challenge of regaining the rest of the gloop so his new alien best friend can medically engineer him back into humanity. I think the phrase 'pear shaped' is one that comes galloping over the celluloid hill at this point. But the ending doesn't disappoint and there are enough shocks and surprises along the way to keep you thoroughly entertained.

The effects, as you may imagine, are rather fine. The eerily floating ship is a constant reminder of the reality of the premise and the South African light does wonders bouncing around this enormous inhuman umbrella. There's never a scene where you question the reality of the aliens. Well, up to a point of course. They are made-up alien prawns after all and the movie's not at all coy about showing them. CG has come far enough now, even on District 9's relatively small budget of $30 million, to be utterly convincing in terms of characters. We have travelled light years from a decade ago and the true misjudged horror that was Jar Jar Binks. Now there's an alien I could be prejudiced against. The location is depressing (as it should be), aliens scavenging where they can, peeing en plein air and generally giving men like Wikus good reasons to treat them like scum. But the design is gritty, the feel of the whole is uncomfortable – again, as it should be. There was never a moment I was disengaged and I will give all oleaginous credit to Blomkamp's old friend to whom he gave the lead role. Sharlto Copley is a revelation. His performance, as naturalistic as it is, is one of a monster who has to actually change species to recant his own awful shortcomings – and what a recant…