if you have any of the DooM games (Doom I, Doom II, Ultimate, Collector's edition, etc...) go download the Doomsday graphics engine. JDoom makes it so that everything is 3D! Even monsters! (after dnloading the model pack).
Works with Heretic and Hexen too!
plus, playing multiplayer is a snap. if anyone wants to kick it oldschool and play some good old-fashioned DM's, lemme know! (supports up to 16 players! instead of 4!)