I've played Unreal Tournament, Rainbow Six, Quake 3 Arena and Half-Life.  Half-Life has the best single player game, that's not in dispute.  Unreal Tournament has all the eye candy and colored lighting along with nifty weapons.  Rainbow Six has the grave sense of realism one shot, one kill.  But for all and out motion and complete absence of pop-up, bezier curves and moving action, Quake 3 is the archetype for everything that follows.