This is definitely one of the more interesting sci-fi concepts I have ever seen.  While the worldbuilding has so many holes and the movie had me almost laughing at how ridiculous the living situations of these people were, it's still a very interesting world to explore.  This movie is at it's best when the audience is shown all of these interesting things in the world that are more or less alien to us.  The characters inhabiting this world are sort of interesting, but not so much.  The story moves along briskly enough so as to not make this a larger issue.  The story/worldbuilding is definitely the best part, and paired with the strong action and drama, make this movie worth watching.  I think the ending was pretty solid, as well as the messages it conveys.  This is definitely not a convential sci-fi movie though, as the film is much more concerned with conveying emotions than letting the audience get to know an entirely new world.  That being said, the movie does kind of succeed where emotions are concerned, to an extent.  A good movie overall, and I will probably watch it again in the distant future.