I first had the chance to play Duke Nukem 3D back in 1997 when I received it with a new computer. It introduced a new level to first person shooters. Humor, one-liners, gore-galore, and non-stop action. If the single player isn't enough, the multiplayer is tons of additional fun.
Shrinking another player and crushing him with your mighty boot, using a jet-pack to rain rocket death on everyone, and freezing your enemies to shatter them were some of many highlights of the many online and LAN games I have played.
The graphics are archaic, but this is how gamers loved it. If you want an improved visual update, there are mods which upgrade everything: textures, characters, weapons, and even the controls.
Duke Nukem Forever is still being made, going on almost 12 years now, but this ought to pique your interest if you missed this gem.