as the title says. you know co-op multiplayer games are really fun I'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 =)
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.
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.
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/
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