It's been 20 years since the aliens--referred to by the humans as "prawns," due to their crustacean-like features--descended into Johannesburg from their crippled mother ship and were forced to subsist in a ghetto called District 9. Parallels with the Japanese-American internment camps of World War ll, and the modern day Palestinians, came to mind. The aliens are exploited by the whites AND the blacks-- the latter having set up shop in the camp to sell cat food and such, which the prawns find so yummy they gobble it up, can and all. (The movie is not devoid of wry humor.)
Wikus van der Merwe (Sharlto Copley) is an agent with a private company (Multi-National United) who, along with MNUs security forces, spearheads the effort to relocate the aliens to another camp. He's not a likable character in the beginning--his methods are callous and result in some alien deaths.
The traditional story arc in fiction dictates that the protagonist be changed, or exhibit some maturation of character by the end, and District 9 certainly accomplishes that. The prawns brought some of their superior weaponry with them, which humans cannot operate because the weapons are matched to the DNA of the aliens. But when Wikus accidently ingests a substance that begins to turn him partly into a prawn, he is suddenly able to fire their high-tech blunderbusses , making him the link between humans and the alien technology. The opportunistic MNU desperately wants him now, and he goes on the run, knowing he'd be turned into a human lab experiment--and killed in the process. Wikus re-enters District 9 a very different individual. In order to survive, he must now collaborate with a particularly intelligent prawn (named Christopher Johnson, just so we the viewers can anthropomorphize him) and his son, who are working on a technology to get themselves and their race free of this planet again.
A battle is looming, and those scenes are as EDGE-OF-YOUR-SEAT exciting and technically impressive as anything we've seen in Transformers 2, or Terminator Salvation--with the added element that we may really CARE more about the plight of these aliens, who symbolize any and all of the oppressed populations of the world.
The only thing that chaps my ass a LITTLE bit about District 9 is that it's clearly set up to segue into a sequel, and I prefer to have CLOSURE in my movies--like, the end is the end for better or for worse. But I'm not deducting any points for that because I'd LIKE to see the sequel to this film--District 9 belongs with the epic tales of how fate sometimes turns ordinary men into heroes. And I find that inspiring as all git-out.