I love DIstrict 9, but I didn't mention it because OP said he didn't want movies with mindless action, and well, I must admit the second half arguably turns into mindless action. It's still awesome, just not what OP was looking for.
A shame the next Neill Blomkamp movies haven't lived up to the expectations.
amok: I quite liked "Sound of My Voice" and "Another Earth", both staring Brit Marling and from 2011. Offbeat and quiet.
If you liked those, you might enjoy
I Origins. It's a different kind of story, but it has a similar atmosphere and there is a mystery lingering around. And Brit Marling is starring too (although not as prominently as in the other two).