I am not an ideal person to review this. I don't like caves, I don't like films set underwater, I don't like the later work of James Cameron (who, to be fair, only 'presents' and produces the film) and I don't like 3D. Prejudices declared, then.
In short, the film involves a cave-dive in Papua New Guinea gone horribly wrong. You don't really need to know any more as the story is ultra-straightforward, with sub-Cliffhanger characterisation and dialogue. And while it's good to see Ioan Gruffudd on the big screen (he once roundly trounced me in a game of snooker, but that's another story), the performances generally involve lots of histrionics, lots of gurning and not much else. The 3D looks good, and the film wasn't retrofitted, which I suppose is positive news, but I just felt very uncomfortable and bored throughout. Don't bother.