Personally, I am not afraid of the dark.
Amnesia: The Dark Descent has changed this.
It is the single scariest game I've ever played, and even now, playing through it for the 11th time, it can still give me the chills. The atmosphere is simply perfect, as you're constantly expecting something to attack you, even in what few breather levels you get. And the best part? More often than not, nothing attacks you... And that just makes it worse, because you know that the longer it takes for something to attack you, the worse it'll probably be when it does. Even before you catch a glimpse of a monster, you're still holding your breath whenever you turn a corner or open a door.
The sound is just perfect, with soft music that you barely notice, hallucinations of footsteps around you, and the disgustingly freaky sound of the protagonist grinding his teeth that you hear when your sanity gets low enough.
However, that being said, the story itself is a little... Well, stupid, to be honest. Up until a certain point, it's all fine - the protagonist (Daniel) erased his own memories, so we can assume something has been going on, especially when a note to yourself informs you that you have to kill the Baron of the castle, Alexander. From there, it goes into the story of why Daniel is there and why he must kill Alexander. In the 3rd part of the game, this story just kind of seems to give up, and dives into a pool of clichés that most would probably have seen coming. It feels as if the creators spent months and months coming up with the best ways to scare people, the scariest sound-effects, the best physics you can get for a game... And then at the last second remembered that they needed an ending for the game and tagged this one on.
This, however, is not bad enough to distract too much from the actual gameplay, which is simply amazing, even if it basically boils down to "Find Alexander. To do this, solve puzzles, go through dark rooms, and occasionally hide from monsters as you have no way of defending yourself whatsoever".
In short, Amnesia is, in spite of its flaws, very much a game worth playing, especially if you're just out for a good scare.