Surprisingly good.

Rating: 9/10 (20 August 2009)

I went to see it knowing only the basic premise - that alien beings were being kept in a sort-of refugee center. And when I saw the first aliens, the first thought that popped into my head was, "They look a lot like PREDATORS." As someone else said earlier, this film "borrows" a lot from earlier science fiction classics. And that is why I took one star away from the film. Other than that, I was mightily impressed.
Actors didn't sound like "actors" - mouthing out meticulously scripted lines. The actors sounded like "regular people" caught up in a dilemma that strained the boundaries of humanity and humaneness. And the central figure who came in contact with the alien "liquid" substance was forced to choose between allegiance to two species.
Beyond that, I'll say no more since it might be construed as a "spoiler" comment. Suffice it to say that this film will satisfy every expectation of the science fiction fan and, in some cases, will exceed them. If you like science fiction (and have a strong stomach), you owe it to yourself to see this film.