One of the best of its kind. Mature themes, gorgeous CGI, somewhat surreal cinematography that flows a lot in unnatural, unconventional ways (no doubt only possible without using the actual real camera). Not a masterpiece, but for what it is (a mainstream 3D-animated kids movie), it's pretty stellar. I liked it as a kid, and I think I'm liking it even more as an adult. Which is something I can't say about most kids movies. Though a little idealistic in its resolution of conflicts, it conveys the "otherness" of the human civilization in this world, and makes you reflect upon our own place in the larger universe.