Counter Strike GO is pretty good for the price. It has a steep skill learning level which keeps it as one the most competitive games to exist. It can get really addicting when you're on a roll and it's really cheap. That or you could try Mass Effect 3's mp if you want something deeper with classes and customization even if it's only co-op and not PvP.

PlanetSide 2 Alien Swarm Tribes: Ascend All three of those are shooters you can play for FREE, and they're full-fledged games, make no mistake. PC exclusives, but definitely worth your time to check out. Alien Swarm in particular is a real gem; think a top-down version of Left4Dead with aliens instead of zombies, and PlanetSide 2 blows Battlefield 3 out of the water... 2000 players per map, I'm NOT joking. As for shooters that cost money, I can definitely recommend Natural Selection 2 and Nuclear Dawn. Both are RTS/FPS games where one player on each team builds structures to support the troops on the ground... really fun games, but again both on PC. If you're going to limit yourself to Xbox, I'm afraid you're stuck with little more than Halo and CoD and a watered-down version of Battlefield.

You could try Arma if you don't mind some extreme realism or you could try Arma 2's DayZ mod which is another game entirely.

Counter Strike Global Offensive or Shadow Run. Both are similar and very fun.

Gears 3 is fun and a nice change of pace. I mostly played CoD and Halo and I'm having fun taking a break with some Gears.

TF2 :)

Tribes? Quake Live? There are a hell of a lot of good competitive shooters on the market. Search for a bit.

[quote]Halo, the only multiplayer shooter I used to play, is utter shit now.[/quote]Pretty skewed standards.

Ace of Spades classic (the free one). It's bloody amazing.