Doom 3 is a Sci-Fi Horror master piece. I've actually jumped back in my chair during parts because of how realistic demons come around corners and jumping out of the shadows. I also can not play it with head phones because it's just too creepy with sounds all around you, and whispers of children coming from empty hallways. You can hear pipes rattle randomly, and feet move on the metal grates near you, which cause you to actually look next to you and behind you in the game and in real life.
This is the most amazing looking game ever right now. It all has to do with lighting. Dark shadows are finally completely black that can hide you or your enemy. When you walk by bright lights on walls your shadow stretches across the floor up the other wall. Not just some default shadow, but you can see the weapon you are holding and details of how you are walking and moving. When you walk near faint lights, blinking lights, or LCD's the glow reflects off of you and the weapon in front of you. The flash light you have will be bright close up, but dim as the objects get further away. Lighting in video games will forever be changed and be more realistic then ever.
If your computer can support it, or if you have an XBox, you MUST get this game. I've just loaded the maps and walked around by myself staring at the lights bouncing off different surfaces and trying to catch my own shadow. Now I know why dogs and cats can be so amused by these little things.