First 'true 3d' FPS? Well good people, that would be the oft-forgotten Rise of the Triad which I recall getting from dialling a BBS in the states just before the xmas of my 14th birthday (1994). It had 'true' 3d in that you could have rooms above/below other rooms as well as ELEVEN player multiplayer... I recall being somewhat blown away by it at the time. NB: Oh yeah I also remember it had the most EPIC god mode cheat of any game. Not only did you become invulnerable, but you could also float at will and shoot 'god-smiting-balls' which insta-gibbed any enemy.