It's a great, not-to-be-missed and very original and imaginative piece of scifi. It's got exciting action set-pieces. It's moving and emotional.
Yes, we are starved of good mainstream action movies, but do we need to go that far as to heap over-praise on Neill Blomkamp's watchable but ultimately a little disappointing movie about an alien apartheid? Really, despite being mildly entertaining and more engaging than today's (below) average scifi action movie (TF2: ROTF, anyone?), District 9 dares not venture further than its initial premise, a premise laid out more than carefully at breakneck pace and in a mockumentary style. But in trying to streamline the story and focus in on the two main characters, the movie then starts to lose the poignancy, built up in the first half, by filling up the spaces with said action set-pieces and shoot-em-up, chase-and-run moments, and stumbles towards more mediocrity by employing the oft-used shaky cam sensibilities. The only thing that keeps us interested is not the big apartheid allegory but the almost voyeuristic and fetishistic need to find out what will further happen to Wikus, or rather, what other parts of his anatomy would rot off.
While its nuts and bolts are fashioned after the likes of Independence Day (hovering spacecraft, also TV series V), Brundle Fly, ET the Extra-Terrestrial, Aliens (the robot suit) and Alien Nation, the theme is just another incarnation, most notably of the rarely-mentioned Enemy Mine, starring Dennis Quaid as a human and Louis Gossett Jr as an alien.
Unlike Enemy Mine, in the end, Wikus doesn't really reconcile with the aliens through better understanding of who they are and what they do.