One of the trio that started it all!!!
Wolfenstien 3D: This game was what created the concept of the FPS shooter and actually attracted it to people. What's better than fighting a robotic Hitler with a machine gun?!?!?!?! The game's concepts were ground breaking. A 3D game that actually involves an atmosphere that isn't linear was an idea that had been around for awhile at that point, but it had just never been perfected.
Doom: The game that launched the multiplayer FPS revolution. I can still remember playing Doom against my bothers with 3 computers hooked up on a LAN connection. Doom was the game that introduced the "Deathmatch" concept to FPS, and even more importantly, created the ability to play a FPS with your friends.
Duke Nukem' 3D: Some would argue that this is hardly a fit to a trio of granddaddy games for FPS, but anyone that would is certainly failing to see the elements that it brought to the table at its time. The major revolutions that DM3D brought forth in the FPS genre were astounding. Introducing the ability to jump, enabling mouse movement capability, the jetpack, and of course, actually being able to blow away cover. (In very small cases) But most of all, DN3D was the first game that actually PERFECTED the multiplayer element to FPS. It was the first game that ran consistently stable, for hours on end, playing up to 8 people at a time against each other, flawlessly.
Beyond any doubt. This game, and it's two trio counterparts, rightfully deserve a place of honor in any true PC gamers collection, even if they do collect dust at this time.