After the climax and near the end, when the human villain was torn to pieces by aliens, someone in the theater cheered and applauded. It attested to the the achievement of Neill Blomkamp that by now our sympathy was firmly on the aliens' side against humans --- and the aliens weren't even cute or particularly anthropomorphic. Buggy-eyed childlike E.T. they ain't, although they did like to eat cat food.
It is not easy to feel all warm and fuzzy about humanity nowadays. Perhaps the world has always been violent and dark and depressing, but meanness and cruelty have never been so vividly exposed and close to home since the 1970s.
The movie left out much explanation, although perhaps that was not a fatal deficiency, since the main narrative was carried out from a pseudodocumentary/newscast
One could argue that white men ruled South Africa for a hundred years while locals were the population majority. Yet the local Africans were not able to overthrow the white rulers during apartheid. Perhaps Blomkamp understood the power dynamics too well, and we understand very little. Nevertheless, one problem was that the aliens had guns --- and pretty big guns at that. It was mentioned in passing that they seemed very passive and unmotivated with no leadership. I think this element deserved better explanation.
If one were to flip the premise around, it was a familiar story --- If humans were the weak minority fighting for survival, like "Planet of the Apes" and "The Terminator". By turning the cliche upside down, it is a reflection and perhaps an accusation on everyone. Rather than celebrating the "human spirit" and thus winning instant allegiance from the audience. The moral position in this movie had to be fought and earned. Yet earn it did.
A sadness permeated to the core of the movie, amidst all the blood and gore and flying limbs and severed heads. It was the realization that this was not a story about the near future or about alien invasions or about fictional thrills, but rather an allegory about our time, our world, and us.