Children of Men was a huge breath of fresh air to scifi films. Tight movie, shot intelligently, interesting cinematography and storytelling. District 9 isn't quite as solid or well polished, but it's a thoughtful and entertaining film. Worth seeing in a theater as an antidote to all the garbage American action flicks.
Both films are grimly depressing. But they're not simplistic dystopian future films where the horrible world is comfortably distant from today. The world in these films is terrible now, today, for identifiable reasons. It's a very pessimistic reflection on our current society. It works quite transparently in District 9's case, drawing directly on apartheid experience to tell the story of what would happen if indigent aliens came to Johannesberg and squatted there in shantytowns. Basically the director is expanding on his short film Alive in Joburg, taking good advantage of his $30 million budget and less good advantage of a 112 minute running length.
District 9 is strongest at the start setting up the world. Excellent use of documentary-style filmmaking and lots of shaky-cam to reveal classic unthinking xenophobia of various stripes. The movie then goes on to more of a classic action flick with slightly irritating Enemy Mine moralistic overtones. It works pretty well though, doubly so because Neill Blomkamp applies his CG background to some really great mech-suit and giant spaceship scenes.
If District 9 is a success we can no doubt look forward to District 10, a Roland Mmmerech / Michael Bay $200M production. The explosions will be bigger, the action sequences will be edited to a frame of their lives, and the soul will be completely gone. In the meantime maybe they'll be making good scifi films somewhere outside the US studio system.