Amnesia: The Dark Descent, a first person survival horror. A game about immersion, discovery and living through a nightmare. An experience that will chill you to the core.
Not only is this one of the few horror games I've played that has been able to illicit pure fear, but it does so without the use of cheap jump scares. Suspense and tension are used masterfully, combining visuals and sound perfectly in the ideal horror experience. This is reinforced by a story that is very well written and paced, with intrigue and mystery driving the player onward.