It's very rare that I find a game that actually frightens or unnerves me. Usually games which are specifically designed to this (read: Resident Evils, Silent Hills, Eternal Darkness...) fail miserably (not that they are bad games). However there have been a few titles which surprised me with their ability to frighten. I'm interested in knowing which games have had the same effect on you.
Here are my nightmares:
Thief - The Dark Project (PC)
The most immersive game I've ever played combined with extremely realistic audio and truly frightening zombies, undead, and mindblowing locale.
System Shock 2 (PC)
The tension this game induces is incredible. A binary nightmare.
Alone In The Dark (PC)
The plot became more and more insane the more you unraveled it. The ambient sound effects still freak me out.
I had this game when I was 10. Not only did it's puzzles bewilder my young mind, but the music and monsters molested it.
Sweet Home (NES)
Despite it's graphical limitations, this game WILL unsettle you. The score is creepy and the monsters random and violent. Not to mention the haunted mansion you're in with all it's illusions and traps.[/img]