While I have no real problem with Mass Effect multiplayer,
Personally it just comes across to me as something that has been shoe horned into a game that didnt need it for reasons other than making it a better game.
Actually I read an interview the other day where they described the multiplayer missions as you going in to finish what Shepard started. The single player game seemed secured the objective, but the multipl player goes in as it is clearly not over. I didnt actually like that as it gave the impression that the single player left things unfinished.