I remember one time I visited my cousins and we played the multiplayer vs portions of Teen Titans for the GameCube. Invariably, it came down to who could get to a certain character first, and then during the fight, just mash down the ranged attack button. However, the game was still fun, despite this obvious flaw.
When you play a multiplayer game, it really is not about the game at all, it's about the people you're playing with. It was fun just to hang out with those cousins, who I hardly ever see. Multiplayer has a way of bringing people together. If you can get so many people in the same room all there to play a game, then there is obviously a deeper connection than the game. I didn't visit them just to play Teen Titans, I didn't even know they had the game, I visited to see my cousins. Also, using multiplayer to facilitate a gathering can lead to a distraction from the awkward parts. Multiplayer is also about forming bonds with people. People set up events just to get people in the same room, playing the same game because of their common interests and, most likely, friendship. By demonstrating your similar interests, you can become closer to other people and players.
This is one of the reasons I've always been wary of online multiplayer. You never really meet the other players or get to know them, so any real bonding is out of the question. It can be fun, but you never know someone till you have meet them face to face. Yes you may add someone to your friends list and you may see them again in the game, but you don't really know them. You're playing the game for the game, not to be around other people. Do people play MMOs to meet people, or to kill dragons? Do people play online shooters because they want a connection, or because they want to show their supremacy in the game?
Multiplayer is fun not just because of the game, but because of the people you are playing with. Online multiplayer games can't replicate being in the same room as someone playing a game.