The Descent is about a group of thrill-seeking women who decide to go spelunking in a remote cave. They get pretty deep into the cave before they realize how dangerous their situation is. The tension is high and unrelenting, and then the monsters come out.
What’s nice about this film is that it doesn’t waste any time whatsoever on superfluous scenes. The script is concise and direct: only the necessary scenes are included. This is a “pop out of the dark” movie, and after a while there is a definite rhythm to each scare event, but the film never becomes trite and it never really loses its ability to startle you. The characters are developed just enough to make the interactions between them important, and the monsters are not dwelt upon for longer than necessary.
It’s been a long time since I’ve seen a pop-out movie that is this effective. Though there are a huge number of films in this genre, very few are successful (Alien is probably the best of the bunch). The Descent is tight, simple, and expertly constructed, and I found it much more effective than I was expecting.