soulgrindr: Also, if you fancy playing Doom, Doom2, Heretic, Hexen etc.. with real lighting, transparency and mouselook then check out
http://www.doomsdayhq.com/
You need the original game files, but it works and looks pretty good.
fuNGoo: Bah! The blocky 3D models pretty much ruin the look and feel of the original. Kind of like what the Hi Resolution Pack did for
Duke Nukem 3D.
ZDoom on the other hand, updates Doom (also Doom 2, Heretic, Hexen, etc) with technical improvements like mouselook, higher resolutions, jump/crouch mechanics, and more but pretty much keeps the look intact. However, if a proper remake with hi poly models and an entire overhaul of the graphics engine was done while keeping the same level design and gameplay, then I'd be totally for it.
But maybe Doomsday offers the classic look too?
By default it doesn't update the sprites into full 3d. There is a pack you can download to do that, but i'm currently playing doom2 in old-style sprite mode. What it does do is add filtering (so you can almost upscale it a few resolutions) and realtime lighting (which actually makes it look way better... having 10 or 20 red and green fireballs flying around actually looks pretty pretty. You can also choose to enable jump, etc..
I haven't tried the 3d models pack (yet), but i think its worth it for the lighting, smoothing and mouselook alone.