Halo 3. COD(both 4 and WaW) have spawn problems, and they will have you join in the middle of a game when your team is about to lose, giving you a loss for nothing, Also, if the host turns off his X-Box, you are taking back to the lobby and everyone gets a loss. Why these problems haven't been fixed, I will never know.
Don't get me wrong, they are both good games, and they have a lot more features than Halo like perks and classes, but in Halo, all the guns are equal, and the matchmaking is much better IMO.
The only other FPS's I can think of is Battlefield:Bad Company, which is a great game but not many people have it and it is an EA game so the servers suck, and Farcry 2, which is much more for the single player.