I've always liked playing Co-op games. Very much in fact, they do give a totally different experience than doing the game solo, or playing mmo's (which could be called co-op i certain ways) Sadly i think that there are too few of this type game around.

I got Left 4 dead couple of weeks ago. And i must say i have had so much fun i that game playing with my friends. It forces you to work together if you want to live or win as zombies. And all those funny situations, just brings in a good mood. And the point system doesn't really focus on one player, but just to shiow which team did better in the end. And this is really important i think. Its just plain fun, and theres not many ragers in the game, like i see in soo many other multiplayer games. There's actually alot of ppl playing who are happy all the way thru even tho their team is losing.

I've played other co-op aswell, and the fact ur often playing with a friend, can make a game which is not so spectacular in it-self to actually being very much fun.

I hope the succes of Left 4 dead, has left thougts in the heads of developers, that this is a very overlooked thing to inplement in your game. Theres so many single players games that would have their experience hightened by x2 if u could play em thru with friends, even tho they might have been an awesome experince as single player.

Well that was my point of view :)