Wikus is wonderfully unlike the standard movie hero. Typically regular-joe-to-hero stories have a guy who's a bystander or a complicit-but-tangential participant immediately flip out and become a selfless moral paragon as soon as he witnesses an injustice being done to other people. "No," says District 9, "that's not how real people act." Wikus is mired in evil and he doesn't care. He's acting purely on selfishness and desperation for the bulk of the film. It takes Wikus nearly two hours on screen to discover the heroic impulse to altruism, and he only does it once he's been so broken down, feeling like he has nothing left in the world and only seconds away from death. Only then can he pry himself off the ground and stand up selflessly for others. That's fucking big, yo. That one moment (and everything building up to it to make it work) is some of the best character development I've ever seen in any movie. And it's a huge sacrifice because Wikus is giving up something that, for most people, is bigger than life: he's giving up his whole identity. Wikus finally discovers altruism through giving up on himself.
Wedded to that is a larger-scale dialogue about how all of us treat the distressed -- refugees, the homeless, starving "third-worlders", &c. Sure, we sympathize. But they're dirty and frightening and alien to us so we keep away from them and care about them on our own terms -- from a distance and only when it suits us, just like the academics and protesters in the film -- and ultimately our sympathy amounts to nothing because we refuse to engage. In the whole story, only Wikus can overcome that distance, and only because he has all comfort and security and identity stripped away from his own life.
Compared to the theme of other films, especially other sci-fi/action films, this is amazingly, singularly thoughtful.
-- Alex