When you get doom try jdoom
http://www.doomsdayhq.com/
This gives you full mouse look, 3d models for all the enemies and pickups, support for up to 1600x1200 resolution, all of the textures have been redone, dynamic lighting and particle effects.
This has been done for heretic and hexen as well as doom and if you look at the screenshots on the link they are very impressive (considering the age of the games)