I am big fan PC games especially FPS (First Person Shooter) and Sci-Fi / Horror. I have to say DOOM 3 is the creepiest game I’ve ever played. DOOM 3 is a horror masterpiece.The more i played ahead in the game it was like crawling inside my skin. I used a nice headphone instead of speaker which made is more awesome.
The first thing you would notice about the game is that it’s too dark. So dark that sometimes you might be standing right in-front of the creatures (in dark) and you see ‘em unless you use your flash light. The use of flash light is another new thing in the game. You can’t attach it to your gun, meaning either hold the gun or the flash light. This changes the game play drastically. If you had a flashlight mounted gun you wouldn’t mind going inside a dark room but when you have to switch in between it really sucks and it’s scary. you go inside with flashlight, you are making your way through and suddenly a creature jumps in front of you, you immediately switch to gun and now you can’t see it. you see why this game is so scary.
Another thing that makes it more scary is the audio effects. It slowly builds a psychological state of mind that you start to feel that you are really there. Whispers, sounds of insects crawling, sounds of spiders attacking you. growling. Sound is everything what makes this game so damn scary.
There were time in the levels that I was actually afraid to play ahead or I would at least remove the headphone or reduce the volume. Kudos to the design team and whoever came up with all those scary creatures like burning flying skulls, spider babies, skull spider etc and these are small but they always attack in large number 
. There are also a lot of huge and very huge monsters and the sound they make….. it just stays inside your head all the time. here checkout this link for DOOM monsters 
Whispers, it makes things very spooky. for example your going through a hall way and suddenly you hear whispers of a women and then babies crying and lights starts to flicker. Whispers are so real with headphone it feels like the spirit is just by your sides. They show you what happened there and they also guide you.
A noticeable thing is that DOOM 3 uses a lot of daemonic symbols made out of fire like crosses , pentagon, star inside a circle. These symbols are mainly the entry point of monsters. The moment you hear a scary voice/sound and these symbols stars to appear on walls and floor you better prepare yourself. I feel these symbols have a psychological effect on the player and from the games perspective it really helps to notch up the horror environment besides the skeletons, blood everywhere and flesh sticking all around
There is so much more about this game that can’t be described in words. You can’t feel it unless you play it.
PS. Doom 4 has been announced
