I thought it was pretty good myself, if a bit... one-note.
The story it told, it told well, but somehow from the reviews I was expecting something a little more complex and multi-layered. There didn't seem to be much more to it than "The way these aliens are being treated is wrong!" which it then hammered away at for another 2 hours. And it did become too much of a conventional scifi/action movie at the end.
Still though, I did appreciate that the main character wasn't just your standard, noble good guy. And the journey he goes on IS pretty compelling.