This has become one of my all time favourites. There has been a few caving horrors out in 2005-2006 and I've seen a couple of them. This one is the best of them by far.
I'm not easily scared by movies but this one truly gave me the creeps. It had me glued to it the whole way through and was intense from start to finish. It doesn't have a boring a moment.
If you're a little hesitant about watching this because you've seen a couple of the others already, just check it out. You'll be surprised. I watched this before the others and none of them match The Descent, not even close.
Suggestion: Watch in the dark. Very dark movie. Daytime watching causes glare.