I've never been scared to play a game before.
If you play this game you gotta be able to crank the sound and have at least decent stereo effects.
I had a blast playing this. This is Doom at it's best, this is what Doom is. Battle against things from Hell on Mars in tight quarters with a very atmospheric setting. More than any other game it feels like you are actually in this situation. That probably comes from the fact that the graphics are absolutely stunning and the sound is top-notch.
Gameplay-wise, get used to working your way around with a flashlight and then quickly switching to guns and blasting into the darkness hoping you are hitting what you saw with your flashlight. This whole aspect really adds to the fright factor, but can get annoying.
All in all, don't expect too much in terms of revolutionary gameplay, but do expect one of the most atmospheric video game experiences ever. Let's just put it this way, if we ever colonize Mars and our colonies are built like the ominous station interiors in Doom, I'm not going.