...and as far as this not scaring people, I'm not so sure about that!
If anyone is desensitized by pretty much everything, it's me. I'll browse rotten.com, watch beheading videos, and watch horror movies almost every day of my life. Not one movie has ever scared me; not even remotely. The Ring? Pshh, a child's movie. The Exorcist? Booooringgg...
But Doom 3? Scary. Silent Hill 2? Scary (Toluca Prison, anyone?).
It is much different if you play it with various distractions, like other people in the room, or even in the same house as you. I was showing someone how scary the game was, but it wasn't the same with them there. You're not as drawn in as if you played this in the dead of night w/ your sound cranked up.
My girlfriend is away till the end of August, so I have my house all to myself. When she comes back, I'd imagine the experience won't be as terrifying.
Hell, I might even move my stuff into the basement (so dark your eyes will never adjust to the darkness) to kick the horror up a notch