My first FPS, well actually second apparently but I can't remember the first. Used to play it at lunchtimes at school on LAN, we'd usually have two machines running Doom and a third running either Doom SP, or Civ.
Many lunchtimes spent in Deathmatch or occasionally Co-Op, doing things like luring the Cyberdemon into a lift or telefragging my opponent.
First place I heard of 'Camping' or the WASD setup, or as it was known to us at the time the 'Quake configuration'. Good days, good laughs.