I'm currently playing a game called Amnesia: The Dark Descent. It's an action/adventure and survival horror game for the PC from the makers of Penumbra. This is probably the most terrifying game I've ever played, blowing the best of other series like Resident Evil or Silent Hill right out of the water. The game is set in mid-1800s England. Your character has Amnesia and wakes up disoriented somewhere inside a dark castle, knowing only his name (Daniel) and his place of residence (Mayfair). Early on into your exploration of the castle, Daniel finds a note that he wrote to himself earlier explaining the he necessarily induced the amnesia, that his objective is to kill the castle's master (a man named Alexander of Brennenburg), and that he is being chased by a "living nightmare".
There are monster dispersed throughout the castle. Daniel has a health bar, which monsters can drain when they attack, and a sanity bar, which drains whenever you spend too much time in darkness, spend too much time looking at monsters, or witness a horrific event. Low sanity causes Daniel to hallucinate and become more difficult to control. The lower the sanity, the more severe the hallucinations and the loss of control. Daniel will pass out if his sanity becomes low enough. There are no weapons in the game to fight the monsters. Once you've been spotted, you have to evade them by running, hiding, or barricading them or yourself until they lose interest.
The atmosphere of the game is the real kicker here. The game makes heavy use of the interplay between light and darkness. It's a rare thing to have the path ahead of you be sufficiently illuminated to plainly see everything on the path. As you are walking, you will hear footsteps that do not belong to you, doors opening and closing on floors above and below you, and even the occasional screaming victim of some unknown torture in the distance. As you progress, doors in front of you might open, slowly or rapidly. Sometimes the wind did it...sometimes not. Even the wind is a threat as it can blow out candles that provide precious lighting.
The first link I post is the official trailer, and the superior one, but it has an ad. The second one is ad-less and does a decent job at conveying atmosphere and gameplay, but not quite as well as the first.
link 1: http://www.youtube.com/watch?v=M627-obxNzg
link 2: http://www.youtube.com/watch?v=h-Yu8OJJYmA