Open Water
I know way too many people who hate this movie because they find it boring. I find it terrifying. Yes, you are essentially just watching two people float in the water for an hour and a half, but if you actually put yourself in their shoes, you will start to feel the terror. Most of the publicity came from the fact that real sharks were used during filming, but the real horror comes from the isolation of being stranded in the middle of the ocean. The ending is a real downer too, which magnifies the impact.
