I remember playing Duke3D with my mates over a LAN, and honestly, there's not been a game that's brought more laughter and more pure enjoyment since.
It was released at the same(ish) time as Doom and Quake (the latter being it's peer) and people tended to be Quake players, or Duke players. Both were about as hard and challenging as each other, but where one was dark and brooding, trying to scare you, the other was slapstick, colourful and took the piss out of itself.
Today we see new shooters released onto the market, and they are either war sims or paranormal based games. I would LOVE to have seen DukeForever. I really think it is something that the gaming industry today needs - an injection of humor and fun. Seems to have been forgotten in the quest for better graphics and bigger guns.
I want shrink rays and holographs, and by-god I want jetpacks!!!