This film is a heavy one. The acting is intense and the suspense carries through the whole movie. As Kiera Knightly's first leading role, I must say it goes against the glam sexy characters she so often chooses now. Thora Birch is also noteworthy although her British accent is inconsistent at the best of times. On the whole it was too intense for me, but I guess that just shows that it pulls no punches. The scenes with the trapped teenagers succeed in conveying a sense of claustrophobia and panic leading to despair. Some scenes actually made me a bit nauseous. Daring undertaking for the young cast and shows that monsters, cheap shot scares and gratuitous special effects are not necessary to scare you. I don't think I could watch this again.