The idea of humans meeting aliens or other frightening creatures and turning out to be the real monsters has been done before, but it’s rarely been done better than in District 9 , the new sci-fi film out of South Africa that was made by a bunch of unknowns and comes stuffed with action and emotion and ideas.

In the early 1980s, an alien spaceship came to Earth and stopped not over New York or Washington, D.C., but Johannesburg. The ship just hovers for months, but after humans break in they discover a million aliens, huddled and starving. They’re the workers of their species, whose leaders died from some unknown calamity.

It’s no accident that the spaceship comes to rest over Johannesburg. The film’s apartheid allegory could scarcely be any more obvious, but that doesn’t prevent it from being quite powerful. The aliens, derisively called Prawns, are herded into a massive slum, where they live in squalor. Most people don’t trust the aliens and don’t want them around, particularly on the occasions when the aliens become violent in an effort to eat and survive. Years later, it’s decided to move the aliens out of town, where the people of Joburg won’t have to worry about them anymore, and a Halliburton-type company is given the job.

Vikus Van Der Merwe (Sharlto Copley, in his first film) is a hapless bureaucrat who gets put in charge of the project merely because his father-in-law runs the division. Vikus begins the film as remarkably clueless and insensitive, blithely grinning his way through the destruction of some of the aliens’ eggs. Vikus is given a truly terrible job to do, but he manages to mangle it quite effectively. However, a terrible accident forces Vikus to see the aliens, and the company he works for, in a new light, and sets the film’s main plot into motion.

The film is the feature debut of commercial and music video director Neill Blomkamp, and it’s quite a success. Many former commercial directors try to coast into features by making films that are slick and stylish but ultimately empty. But Blomkamp (who also co-wrote the script with Terri Tatchell) has made a film that is almost overstuffed with ambition.

Besides the obvious allegory, the film never forgets that it is a sci-fi spectacle. The CGI used to create the Prawns is virtually seamless, and integrates them flawlessly into the movie. The image of the spaceship floating over Johannesburg is also very powerful, even when it’s just in the background of a shot, unremarked on. And as the movie goes on, there are some truly huge action set-pieces.

Blomkamp even succeeds at making the movie into a character drama. Vikus begins the film as a truly astounding tool, but his suffering forces him to grow as a person. Watching this growth, as the sadness and horror of Vikus’ situation overwhelms him, is truly heartbreaking. And the relationship between the two main Prawns that we meet, Christopher Johnson and his young son, is very affecting even though both of them communicate with little more than a series of clicks.

The movie is shot as a mockumentary, though it drops the device whenever it needs to, increasingly so as the movie goes on. The format is not really a burden to the film, but it doesn’t add anything, either (although seeing the spaceship special effects in 1980s-quality videotape is quite unnerving). It seems more like a crutch that Blomkamp is using for his first time out as a feature director, but it’s obvious from watching the movie that he doesn’t need it.

His first time out, Blomkamp has imagined a rich, ambitious sci-fi world that strives to be several things at once and somehow succeeds at all of them.