The Descent will scare the shit out of you. Let's get that straight right off the bat. I jumped out of my seat at least three times, probably a lot more. The director definitely sat down and said, first and foremost, before anything else, let's give people a few good frights. It's some scary stuff. (You can always tell a good scary film when you're walking home from the cinema in the dark and you avoid dark patches in the street). And it's relentless. Aside from maybe ten minutes near the beginning of the film, it's almost constantly either ratcheting up the tension or releasing it in an orgiastic burst of violence.
But, frighteners aside, is it any good? I'd say...yes! There's a couple of plot holes, and some of the events seem a bit too conspicuously determined to move the plot in certain directions [for example, I enjoyed the fact that the creatures weren't particularly powerful (in fact, they were pretty much consistently beaten up by girls in any one-on-one fight), but their capabilities seemed kind of random- one minute they're slicing people's throats open with their claws, the next they're literally clawing at someone's back, but not doing any damage]. Oh, and the effects are occasionally ropey. But the overall arc of the film, the acting, the music, the pacing, it's all pretty top notch- I was never unentertained.
So, I definitely recommend it to horror fans. Don't go and see this if you scare easily. Or if you gross out easily- it's quite brutal at times. In fact I dare say this film is scarier and more gory than Alien. That's quite a feat.
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spooooiiiiilers ahoy! (below)
ps- for people who've already seen it, I wasn't particularly keen on the 'fake' ending (that is to say, I the ending, I just didn't like how it was fake), although it did get me thinking, which is a good thing: one way to view the film is that Sarah more or less loses her mind after the cave-in: the creatures are all hallucinations and it's actually Sarah going around killing everyone. On what evidence do I base this? Not a lot. For starters, Sarah is obviously hallucinating when she hears children before the cave-in. She also kills a child and a mother an obvious Freudian guilt-catharsis over the death of her daughter. Then at the end she seems to be having a much more sophisticated hallucination, and you can hear all the creatures around her but, at the end, when the camera pans back and her daughter is no longer there, you can't see them. Anyway, it's a theory. I didn't say it was any good.
Have you heard my Blair Witch Project theory? Okay: The two guys are messing with the girl. It all makes sense. The first guy who disappears is making all the noises off screen. The second guy must be in on it because he throws away the map and stands in the corner at the end of the film. The first guy brains the girl in the last shot. It all ties together.
This is a 
It got a good review in the metro too, and I thought about it, but I scare easy. I'm a big girl.
Based on your reaction to The Ring, I'd recommend you avoid it.
Nice to hear you enjoyed it. It's on my list of things to do this weekend (as it has been for the last two!)
And interstingly, in my own debate about spoilers and reviews etc. 2 things come to mind about your review: one it's worth putting that the collapsible bit has spoilers before the section. and 2, the collapsed section opens when you add comments! D'oh!
BWAHAHAHAHA!
No, actually, good points. Updated.