Crustacean-like aliens are causing problems in a gritty Johannesburg. Disturbing … and yet, says Kimberly Gadette, what a great excuse to open with the line: "Once up-prawn a time …"

This is not just another fish out of water story. For his debut feature film, Johannesburg-born Neill Blomkamp expanded the plot of his original nine-minute 2005 mockumentary, Alive in Jo’burg, in which he introduced aliens to the cultural mix of Johannesburg, South Africa.

District 9 refers to the ghetto in which 1.8 million shrimp-like aliens (disparagingly called "prawns") have been cordoned off from society for twenty years, ever since their spaceship stalled in the air above Johannesburg. But things are getting out of claw, er, hand – the 8' tall, two-legged, catfood-eating aliens are growing in numbers and hostility. Dare we say: surf 'n' turf out of Africa?

A private company called Multi-National United (MNU), uninterested in the aliens' wellbeing, is evicting them to another camp that's even worse than the current shantytown. (The outskirts of Soweto, with its decrepit tin hovels and landfill, stands in for the fictional District 9.) But MNU can't dismiss the aliens completely; the company is after the DNA-specific weaponry that can only be operated by the creatures themselves. They've conducted years of lab research and have so far netted nil. However, everything changes once ambitious MNU field agent Wikus (Sharlto Copley) accidentally comes into contact with some mysterious goo. Before you can say "pass the cocktail sauce," he starts to turn claws-trophobic. Poor guy. He may not be pretty, but he's got a brand new trigger finger, er, pincer that's packing heat. A shell shooting shells, as it were. He's now MNU's most valuable asset … every last piece of him. Literally.

Try though they might, MNU agents can't track Wikus down. Didn't anyone think of putting out a bit of butter sauce?

Hailing from the world of visual effects, commercials and music videos, writer/director Blomkamp opens the film on a stylistic high. He melds hand-held action cams with cinema vérité, as we watch "real" interviews with Wikus' loved ones, employers and industry experts, all lamenting his demise, speaking of him in the past tense. Which, in turn, gives us an early sense of dread. These scenes are cleverly intermingled with earlier, straight-to-camera monologues from Wikus himself, bubbling over about his latest promotion as the newly-appointed supervisor of the alien relocation project. Hand-held cameras follow him as he marches into the District, the perfect low-level bureaucrat wearing a tan sweater vest and armed with a clipboard and a forced smile. He plies the confused aliens with candy and lies, evicting them as one might destroy a nest of cockroaches.

Wikus' victims – CG-created aliens with Scarlett O'Hara sized waists, hard shells, bouncing gelatinous tendrils overtaking the lower half of their faces and deep, soul-searching eyes – are the true innocents. Blomkamp zeroes in on two creatures in particular, a father and son, who carry the heart of the film.

It is no accident that District 9 revisits Soweto, its name practically synonymous with apartheid. In the early stages of the film, it seems that Blomkamp might dissect such topics as xenophobia, the rights of aliens (whether intergalactic or merely illegal), mercenaries brutalizing the disenfranchised, impotent bureaucrats, illegal genetic experimentation, gang violence, underworld operatives exploiting the poor, etc. However, the film soon devolves into an all-guns blazing, hour-long chase scene, the creatures trying to get home while Wikus is stuck in an Iron Man-esque ecto-metal shooting machine. Rather than Tsotsi or Alien Nation … we get E.T.

As Wikus, actor Sharlto Copley does a fine job grappling with, um, shell shock. He's unafraid to show us the eager sycophant who'd probably sell out his own mother if it meant a modest boost up the career ladder. As written and acted, credit Blomkamp and Copley for presenting a deeply-flawed protagonist whose humanity builds as his physicality disintegrates.

Well shot, dramatically paced, with superb production design and locations … District 9 has a lot going for it. But it represents a missed opportunity, the promising story falling flat. Hopefully Blomkamp's freshman effort will be the first of many, far more riveting films.

Rating on a scale of 5 popcorn shrimp: 3

Release date: US: 14 August, 2009 UK: 4 September, 2009
Directed by: Neill Blomkamp
Screenplay by: Neill Blomkamp and Terri Tatchell
Cast: Sharlto Copley, David James, Jason Cope, Vanessa Haywood, Nathalie Boltt
Rating: US = R; UK = 15
Running time: 113 minutes