It's too uneven and juvenile to deliver on its ambitions, and could easily be 20 minutes shorter (a dozen fewer shots of CGI goo hitting the lens would have sufficed), but it's ultimately too blazingly unique to not recommend.
Every once in a great while -- perhaps only a handful of times each decade -- that rare film comes completely out of left field to let us know that there are still some original ideas out there, and that cinema can still be fresh and exciting.
District 9 isn't without its rough edges. It's a bit obvious and doesn't take as full advantage of its premise as it could. But it's also a visually spectacular and cares mostly about its characters, and that's a rare thing in film today.