The scariest game....

Condemned “Criminal Origins”... Released 2006 Condemned offers new scary tactics. No zombies and Mansion, only blood squirting heads

The original resident evil was pretty damn scary when it first came out (I was a lot younger then though).

Resident Evil 3: Nemesis

i would say F.E.A.R

alien for ps1

I own F.E.A.R. and Doom 3, but I haven't tried those, yet...
Someone told me those 2 are very scaring games.

Alien vs. Predator was the scariest game for me.

Obscure

F.E.A.R and Silent Hill 4 are pretty nice

Doom 3 + Night + 5.1 + Console = Scary