What is it that scares you the most about Amnesia?

[Frost]

The audio. I would often wonder if what I heard was a real threat or insanity in my first few hours of gameplay.

The suspense. Peeking around corners, walking down corridors, freakin' opening doors... I wasn't super cautious all the time, but when I got cocky and careless, I soon regretted it.

And, being helpless. Not in the way Hunter of Shadows mentioned (although that's scary too), but being lost in an area made me feel incredibly helpless. The prison was the worst... I didn't know where I was going, where I've been, there's monsters everywhere... aaaugh.

Frictional is brilliant.