not only would it be unscary, but the framerates would drop to zero, the game/textures are pretty, imagine with the lights on that the engine would seem so-so trying to render all the textures at once...id gets to cheat in that respect by allowing just a fraction to be rendered when the flashlight is on.
Everything is rendered even if you can't see them. You're standing in a 7m x 7m room with two monsters at best, it's not like there's much to render.
I've just seen the title of my post is "Re: How's the physics???". Didn't see that post, but I'll answer anyway. They suck.
Physics in DOOM3 are cheap ragdoll (think 3-4 years old effect) and you can push stuff around (again, think 3 years old effects). They're also off in MP.