Oh...boy. This was an awesome movie. A perfect horror film with all the required elements: working on a primal fear (claustrophobia), characters losing their minds, darkness, creepy sounds and just about the creepiest monsters I have ever seen in a film.
I loved it, even if I was completely tense and terrified through most of it. That just means it was effective. The atmosphere is perfect--all small bits of natural light in the middle of a pitch-black cave, barely any music, just sounds and echos that would be terrifying on their own. And one thing I absolutely loved was the fact that, unlike in most horror films, I didn't hate the characters. They were real, therefore a little dumb (like any of us would be if terrified out of our minds), and a couple of them were totally badass, another rarity in horror films starring women. They fought back, and they fought back hard. I liked that.
So another awesome horror film, though I don't think I'd be watching it again--too much of the tension would be lost knowing what's going to happen, I think. But definitely a remarkable movie, particularly compared to the rest of the dreck in the genre, and I definitely recommend it if horror is your thing.
One thing I wouldn't recommend is watching it like I did: alone, in the middle of the night, in a mostly-empty house whose back yard runs right into a mountain. I had to stay up watching Cartoon Network for about 2 hours before I could fall asleep. Because I am a wuss, and yet I love watching horror movies.
It was so much fun.
*And yes, I know it's echoing the Dali photo (http://farm1.static.flickr.com/210/478272835_a91f5e30b1.jpg), and I think that just makes it cooler.