What is the best co-op multiplayer game you've ever played?

as the title says. you know co-op multiplayer games are really fun :DI'm voting out for 'left for dead', and i guess that's the best co-op I've ever played. I used to play it on PC as Zoey with my friends (a sniper rifle and a twin pistol is a good combination, although an autoshotgun is best for tanks). I'm not a big fan of FPS but i love the thrill of survival horror on its gameplay, especially when there's a hunter around =)

......Tom Clancy Splinter Cell : Chaos Theory for PS2...How about make a poll then?

Team Fortress 2 and Left 4 Dead was the best FPS. Transformers ROTF is fun.

The best is Left 4 Deadcannot wait to play with my friends again tonight:)

IMO The Simpsons (the arcade game) is the best multiplayer co-op game ever, simply because i had such fun memories of that game.My sisters and I just spent a lot of tokens playing that game.

Mario Party..oh wait.. its co-op....From memory I doesnt remenber anything usefull. Its very hard to play a co-op multiplayer game.

left 4 dead hands down, no other game lets the players create their own storys!

Left 4 Dead or Army of Two are really the only two Co-op games that come to mind that are good.

co-op...
hmm...
there was this game on PlayStation called Battle Hunter
it was really fun when playing in teams, but I guess it can't compare to games like left4dead

Knights of the Round Table, TMNT: Turtles in Time / Hyperstone Heist, Fighting Force, Joe & Mac 1 & 2, Captain America and the Avengers, all come to mind as some of the best Co-Op multiplayer games I've ever played.

Simpsons on Wii
Far Cry Coop mod on PC
Tom Clancys Splinter Cell Chaos Theorie on DS

Army of 2 for 360
CoD and Resistance for Ps3
Lego games for PSPI never played co-op at DS.

maybe transformers 2 on wii i guess

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Right now Turtles in Time and Contra (I belive me and my brother used to play 3) come to mind.

Red Alert 3, nothing beat teaming up with a good player and whoop AI's butt.

I think this Source-Mod will be great to when its out. Its a complete remake of the original Half Life with new models, textures etc and not just like Half Life Source (Valve sucks at this). And it have a coop-mode.http://blackmesasource.com/

databankI wish I had a buddy to play co-ops with because my brothers aren't generally into games and I have no friends.
But I do remember playing a game known as Lego Rock Raiders many years ago (with my brother-rare moment) and I enjoyed it thoroughly.

OMG! I had that game and it did not worked! LoL I thought I was the only guy who had that game.I am sooo happy right nao :3

Left for Dead ::)

castle crashers! xD