tl;dr version: It's worth watching as a cool action movie that riffs on well-established tropes in a playful, by-the-books kind of way.
Mild spoilers ahead. Nothing serious. There isn't much to spoil, anyway.
2009. Directed by Neill Blomkamp. Screenplay by Neill Blomkamp and Terri Tatchell. Produced by Peter Jackson. Starring Sharlto Copley.
It's super gory. Bad guys get exploded all over the place.
The alien animations are very well done, very convincing, and used appropriately. The level of detail that went into them is marvelous.
As far as the story structure goes: The movie uses the technique of fake documentary to set things up, but drops this when it would interfere with telling the story in a conventional way, whereupon it adopts conventional techniques for dramatic exposition.
As far as the plot goes: It has one original conceit that forms the core of the back story and is revealed in the opening minutes of the movie: Aliens get here but they don't know why they are here or what they're supposed to do. They are desperate and have no unity or organizational structure. They are basically dependent on human civilization to sustain themselves. Nobody knows why; the film offers some conjecture.
That conceit is basically just a pretext for the aliens to be in a big internment camp. From that point on, the movie is like a simplified and superficial version of Focus, boiled down to a bunch of sci fi action clichés. The main character, Wikus (played to great effect by Copley), is a sack of shit patsy shlub who suffers a reversal of fortunes and has the brutal implications of his own stupidity and hypocrisy thrown in his face. He never comes to any kind of insight into his own circumstances, though; he doesn't have much time to reflect, because people are mostly shooting guns at him.
Other than that, the world is divided into a very few Good Guys, an overwhelming number of Bad Guys (who are exploded, but that's okay because we'll just call it comeuppance, it's okay to kill them if they're bad), and an inert population of aliens conspicuously lacking in any kind of voice or perspective. (There's one exception, the alien Christopher, but it's implied that he is a special case and is not representative of the aliens in general.)
It's not about apartheid per se; it's filled with echoes of apartheid, of which setting it in Johannesburg is the most transparent. It is ostensibly about the kind of structural violence of which apartheid is an instance. But it doesn't say anything novel or interesting about that theme. Nor does it tell a consistent story about the motives behind it (at first, it seems to be neglect, but then at some point it's actually about greed and lust for power).
Whatever you might have heard, this isn't a thinky movie and doesn't pretend to be. It's an action movie, with people exploding and cool aliens. It's honest about that. It's not preachy or didactic. It doesn't pretend to be clever. That would have been unbearable, given the shallowness with which it treats the issues involved. This isn't a morality play; Wikus and Christopher are never representative of anything more than themselves. It draws no conclusions it didn't already assume, and it doesn't assume anything radical or interesting. The back story and the plot are occasions for a sci fi action adventure, nothing more. The movie ends on an ambiguous note and doesn't force you to adopt any particular interpretation of what will happen next.
If you want a sci fi action movie with evil humans shooting guns and being ripped apart by bug men or blown into ribbons of gore by bolts of plasma, then you will enjoy this movie. I enjoyed it. Just don't ask it to be anything more than that.