Yeah, I don't get why people are so worried... it's like when multiplayer is mentioned they immediately forget that BioWare has invested much into the story of the ME trilogy and has probably already planned this **** out from the very beginning. It's not as if they're going to completely reinvent the single player in the third game and ruin what the first two have set up.
So what, it has multiplayer.... there are probably new folk working at BioWare who they're pawning this off on to get their feet wet, which is usually the case with this kind of thing. And even if it does suck... who cares, it's not going to effect the main game.
Like Mav said, Uncharted 2 had multiplayer... I wasn't a fan of its multiplayer but Uncharted 2 is a ****ing awesome game with or without it. Same goes for Metroid Prime 2: Echoes... and I'm sure Dead Space 2 will be ****ing awesome whether or not you bother to click over to the multiplayer section of the game or not.