I would say it is Amnesia: The Dark Descent, even though I got bored quickly.
Actually, scrap that thought: the scariest video game was actually a single level from Vampire the Masquerade: Bloodlines: The Oceanside Hotel. It is a homage to The Shining and there are no enemies to speak of (although there are three places where you can die), but you will be paranoid regardless.
[youtube]http://www.youtube.com/watch?v=ztXmBa6mgK8[/youtube]
EDIT: Should have paid attention to this:
One-Winged-Angel wrote:
The hotel mission in Vampire: the Masquerade - Bloodlines
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DISCLAIMER: It should be noted that, while I strongly suspect I have Asperger's syndrome, I am not diagnosed. Nevertheless, my score on RAADS-R is 186, which makes me a pretty RAAD guy.
Sorry for this terrible joke, by the way.