This movie entertains from start to finish. Are the characters "two dimensional"? To me not in any sense (ha ha, yes the movie is 3D, lousy pun intended).
But seriously, for two hours you are taken on a brutal subterranean adventure. I liked the fact that it IS believable. It isn't just action - it is a true human drama and shows the good and bad that can come from people in a life or death situation. And I didn't think it was predictable (for the most part, anyway). I am guessing that the reviewers just didn't like the characters, but that is no fault of the actors; the characters were quite realistic, which I considered a huge plus, while others might have preferred something else. I do need to give a disclaimer that I did not research the "true" story and watched purely from the perspective that it is 100% fiction, so I'm not saying this is an accurate depiction of real events. But it sure seemed like something that could happen.
It isn't "The Black Swan". It isn't "True Grit". It won't be sweeping the Academy Awards. But was it entertaining and worth the price admission? Without question - I actually found it more enjoyable and gripping than anything I have seen in some time. Highly recommended - give it a fair chance!