There are a couple of strokes of genius in District 9 that renew one’s hopes for the future of genre film.

One is casting Sharlto Copley, who’s not a trained actor, as protagonist Wikus van der Merwe, a dweeby South African bureaucrat who has greatness thrust upon him and doesn’t know what to do with it. Copley plays him so unheroically that he could head the cast of a South African version of The Office right now, no questions asked.

In interviews, Copley says he’s dealt with so many dweeby South African bureaucrats that, when his friend, novice director Neill Blomkamp, asked him to play Wikus in the short film Alive in Joburg, he felt he was up to the job. And with producer Peter Jackson’s blessing he stayed on for the feature.

This casting is so effective because we don’t know how to take Wikus as our protagonist in a sci-fi action film. In a cruelly accurate satire of office-dweeb life, sure, but not in a sci-fi action film. I wasn’t even certain he was our protagonist for a long time, and kept expecting him to be sidelined in the course of the plot developments. Copley plays him that way, as a weedy guy born to be sidelined who is befuddled to find himself at the center of the action once the going gets dangerous and consequential. This is terrific, creating all sorts of tension and uncertainty about what’s going to happen next. How long has it been since a genre film did this? I can’t remember, that’s how long.

Which leads us to the second stroke of genius, keeping the film set in Johannesburg. For most of the world this is a nicely undocumented setting, commercial film-wise, so again we don’t know exactly what to expect. We’re on alert for apartheid ugliness, of course, and expect that the aliens will fill in allegorically for the oppressed black population. They do, but in a nicely complex way, becoming the bottom of the totem pole of oppression with every human across the races despising them and wanting them gone. One plot twist involves Nigerian gangsters exploiting the aliens’ addiction to cat food.

There are lots of great odd details filling the early scenes, suggesting we’re not getting all the cultural references, that make for exciting film-watching. Wikus’ thick Afrikaaner accent is enough to put us on alert, our minds racing to get everything, which is exactly what the experience of a film should be. This whole dominant practice of making slow films for dummies is inexcusable.

The film’s backstory, provided in fake-documentary talking-heads style, is that an alien mothership mysteriously appeared above Johannesburg in the 1980s. That led not to an attack on us, War of the Worlds-style, but to an aggressive takeover of the ship by South Africans. Sickly aliens onboard got herded into a temporary refugee camp that evolved over the years into a crime-ridden shantytown. The film’s action starts with the new government mandate to clear out the shantytown and herd aliens into a modernized camp run by the sinister Multi-National United corporation (MNU). Wikus has been chosen as the corporate representative to go notify the aliens of their evictions. His formidable CEO father-in-law got him the job.

These are some excellent sequences, as Wikus goes from one battered shack door to the next trying to get aliens, derogatorily known as “prawns,” to sign their own eviction notices. He’s backed by nasty military muscle, and completely clueless about what’s likely to happen in such a volatile situation. He keeps turning to the camera to joke with the cameramen about the squalid aspects of “prawn” life, as the aliens mill around angrily and the tension ratchets up notch by notch. Nice!

What happens to Wikus there is not expected. Thank you, screenwriters Neill Blomkamp and Terri Tatchell.

This is not to say the whole movie works. It loses steam halfway through, taking on a familiar narrative shape, and the last sequences are fairly straightforward action-chase-rescue-fights. The ending is terrible, a sticky-sweet final two minutes that’s like something out of Wall-E. (Curse you, Blomkamp and Tatchell, if that was your doing!) All the more sentimental or heroic scenes are iffy because the creative team seems uncomfortable with them. Their insight and inventiveness disappears as soon as they have to portray goodness, and they revert to sadly played-out conventions. For example, the lead alien Christopher Johnson (Jason Cope + CGI) is set apart from the other bipedal crustacean-looking aliens and denoted as “good” by having him wear a vest and tattered pants.

Reminds me of The Simpsons Movie, in which Homer protests the butchery of a pig in a top hat, yelling, “You can’t kill him if he’s wearing people clothes!”

Christopher Johnson is also saddled with a small alien-son with ET-like blue eyes. Many painful moments of adorability ensue.

Still, the film has enough fast, lively, shocking material early on to make it worthy of the advance buzz and favorable press.

Though not everybody’s on board. Daniel Engber of Slate argues that the film’s no good because it trots out that moldy sci-fi cliché, portraying corporations as the enemy, which we’ve already seen done in Blade Runner and Aliens and old warhorses like that. Why oh why, bright bulb Daniel Engber asks, are sci-fi films so tiresomely fixated on evil corporate overlords running our dystopian future?

What could be behind this strange fixation? What could it be? What cooooouuuuld it beeeeeeeeee?

Probably some obscure Freudian thing.