An old one, but a good one. Amnesia: The Dark Descent is a great game that uses the environment to scare you and keep you tense throughout the whole game. Just as you're getting comfortable in an area, you discover you're not alone.
The graphics are a little older and certainly aren't next-gen, but the hours of wandering around this creepy castle are well worth it--especially once things start to fall in to place in terms of plot and Daniel's past.
Jump Scare Rating (things that jump out and scare you): 7
Environmental Scare Rating (the need to pee your pants from walking around): 9