If you get anything out of this movie, it should be the alien kid. He is the soul of this movie. He will make you hope the crap out of yourself that everything turns out okay.
Thirty years ago, an alien spacecraft limped its way into the skies over Johannesburg, South Africa. The aliens inside it were rescued like cats from a dilapidated house, and grouped into a refugee camp called District 9.
In that time, they have done nothing but scavenge hopelessly around, with a little help from local gangs.
The cultural differences between these forced neighbors eventually escalates from racism to violence to rioting, so the government steps in to send the aliens somewhere else. Wikus Van De Merwe is the adorably naive nice guy who gets chosen to lead the task force in District 9, where he immediately sprays himself in the face with an unfamiliar canister he finds in one of the shacks. (This is important, but they don't dwell on it. They let the story unfold on its own.)
The movie seems to say that we treat each other so poorly that we would extend a hand in violence even to alien life, a habit they adopt, but the pace is steady and keeps it from getting too preachy. It stays interesting. The story is always a step ahead.
Special effects are worth mentioning because they are used correctly, like window dressing, not the product they are trying to sell.
Having said that, they should have won an Oscar for Most Realistic Display of Guys Getting Killed With Alien Weaponry. It was seriously unbelievable, and I didn't have to rewind it because it happened a lot. But they don't do it for it's own sake. They only blow someone up if they absolutely have to.
See this movie, but not for all that. See it for the alien kid. He trumps any human kid I've ever seen in a movie. (Want a good example? Compare him to the kid in The Mummy Returns. No 8-year-old has been alive long enough to be that smart, witty, resourceful, and unafraid of a mummy.)
This little guy finds his way into the scenes and makes you see the face of unassuming vulnerability, and suddenly you really care about what happens to him. He doesn't seem to understand how dire things are (how could he), he just wants to help his dad and it's inspiring to watch. If he wasn't a made-up alien, he would be your kid.
Let this movie tell you its story. It's as good as science fiction gets.