I recently went to go see M. Knight Shyamalan's recent masterpiece Devil. I'm a big fan of his movies; they all have underlying messages that most people don't understand or even try to. I think it's because he usually markets them in an unfitting category. Most of his movies are thought-provoking psychological thrillers with elements of horror and sci-fi. However, none of them are truly scary. It's nothing more satisfying than to leave a movie theater feeling like you've learned something.
Devil, falls in the same category as The Sixth Sense and Signs as far as "scare factor". I think most people are afraid of the title more than anything else. The movie focuses on the power of confession and forgiveness. If you value those factors and can get past a few loud noises and scary movie tactics then Devil is a must see!