I don't remember WHICH famous Science Fiction author said it, but I remember the quote:
"The best science fiction stories are about the problems of today."
Clearly this film was full of metaphors for apartheid, which may technically be over but you can also stretch this metaphor to any other situation with transplanted refugees (think Darfur, for example). Governments take them in because it's the "right thing to do" but they end up being treated terribly anyways. I thought this movie was very pertinent.
I also think any sci-fi movie changing the roles of aliens from our normal faceless destroyers to something different is a good thing. Buck you, Hollywood. This film switched the tables a little bit, essentially putting human beings in the role of the bad guys and pushing the viewer to, instead of just focus on the awesome special effects, consider how we would really behave in a situation like this.
Normally I'm like that old commercial "Hey, you got summer blockbuster in my deep movie!" "No, you got deep movie in my summer blockbuster!" but I think the director walked the line.
Most impressive for me? Tom Cruise and Nicholas Cage weren't in this movie. IE it had big budget production values, but none of the terrible acting we normally have to suffer to watch it.