According to one writer, seven games parented the genre of the multiplayer FPS. Halo and Call of Duty: Not on it. Ed Borden reasons they did not add gameplay innovations, merely perfected the themes. That's up for discussion (and why I'm posting it, of course), but a fair point.
The seven titles we owe it to: Doom, Quake, Tribes, Battlezone, Unreal Tournament, Counterstrike and Battlefield.
If nothing else, at least the past two or three years of FPSes, multi- and single-player, have combined to give us standardised controls, which makes picking up a new title infinitely easier to play — especially when it comes to free looking. It's now pretty much left stick = movement, right stick = head, with no fruity switching of camera angles or other unnecessary twists. Also, Y or triangle is use, B or circle is jump, etc. If you think that's a minor gamer assist, ask yourself the last time you used two different copiers or fax machines with the same set of commands.
Ed also argues that single-player FPSes are constantly delivering great new titles, but multiplayers have been "the same old for quite a few years now." I just can't see it that way. Maybe structurally they are the same, but characters, missions, game story, that's what gets me into an FPS now. True, a new gameplay innovation that's widely adopted will beat the best written game for sales, but I ask you, what else could a multiplayer FPS be doing right now?