Amnesia: A Dark Decent
On paper, this PC survival game doesn’t sound too bad: find your way out, regain your memory, avoid enemies and solve puzzles. But put yourself in the dark and terrifying environment within the game and you’ll soon see why it’s got the reputation for one of the scariest games ever made.
One of its main gameplay features (and possibly the reason why it’s so creepy) is the fact that if you’re left in the darkness for too long, the protagonist begins to lose his mind. This affects what you can see and also lures enemies towards you. Equally, standing in the light for too long will draw the attention of the monsters. Not only does that make you feel trapped but the fact that there are no weapons within the game will make you as the player feel even more terrified.