If anyone still remembers Duke3D, which in my opinion is one of the best, if not the best, 3d shooter ever made, then check out this site:

http://hrpupdate.duke4.net/

These guys completely re-made duke3d, added new texture, new models, new sounds, 3d acceleration support, etc. Right now it's graphics are about Quake3 quality, if not better. Check it out.