First-time director Neill Blomkamp based the film off a 6-minute short film he made called Alive in Joburg. The pseudo-documentary style, which was later used in District 9, features a number of interviews with South Africans about their feelings towards the aliens. In Alive in Joburg, most of these interviews aren't fake; they're actual interviews with real South Africans about their feelings toward Zimbabwean refugees in the country.
This realism carries over to District 9, where the slum the "prawns" are forced to live in wasn't created for the film. It was a real recently-evacuated neighborhood of impoverished housing, and like the prawns, the real-life residents of these shacks had been evicted to move to government-subsidised living areas.
What really sticks with me is the performance of Sharlto Copley as this human main character, Wikus. At the beginning of District 9, he's a huge dick. A weaselly Afrikaner paper pusher working for a shady multinational military contractor, he's assigned to lead the relocation of the prawns from Johannesburg to a giant internment camp outside the city. He looks down on the prawns, laughs about killing their babies, and in general represents greater society's negative view of the (literal and figurative) aliens. He's the worst kind of person.
Over the course of the film, though, we as the audience empathize with him. But it's not because he ceases to be a douche. He doesn't. Even when he sticks it to the Man and helps the aliens, it's only because he wants them to help him in return. But it's those shades of gray in which we find his humanity. What District 9 accomplishes beautifully, other than the sweet Afrikaner accents, is this idea of finding the good in the bad.