Well, since the overwhelming string of posts seems to be leveled firmly in the 'It's the worst thing since ET the Game' camp, I'll point out the possible way of doing it that would be really cool, cutting and pasting my own comments from the last time this came up and everyone started whining in the thread about the pre release options;
Funky thought, what if 'multiplayer' means the ability to have two other players playing the rest of your squad through a mission? Not just the fighting, but also the cutscene/dialogue wheel segments? The host playing as Shepard while the other two play as the squad members of their choice, getting to chose the RP options for Garrus or Wrex during a cut scene would be pretty cool, getting to integrate the role-playing of all three players into one unique cut scene.
Or...maybe...every player has two characters, one is their Shepard, the other is their 'multiplayer character' You create them to fill a niche in someone's lineup if they want to do an online segment with other players. You'd get the opportunity to create a character of any species, Krogan, Turian, Quarian, etc, flesh them out just as completely as Shepard. Maybe a background, key points and personality segment for each that dictates their speech options during the cutscenes. Your multi-player characters would develop just like your Shepard, but there would be a different skill tree and bonuses for playing them that you couldn't access as Shepard. While on the inverse, you'd receive bonus XP for hosting other players, and you'd have aspects of your skill tree that would only be accessible to Shepard. It would give you an incentive for playing as a host for a multiplayer segment so you can level up faster and gain bonuses for your play throughs with bots, while you'd gain a different roleplay and combat experience playing as a squad member.
You could throw in a command role for Shepard and XP bonuses for the team members for fighting as a unit and completing objectives that your lead Shepard set. Plus you'd get the chance to play as a Krogan Warrior, or a Quarian Marine, or any of the numerous Citadel Races that we've seen as supporting characters at best and the Fanboys are desperate to see more of.
Conceivably you could play through the entire game as a 'backup squad member' building XP with your character and seeing the adventure in a different light, being a part of a different 'Shepard experiance' for the finale of the game. Perhaps there would be an option for players to form ongoing parties so that they could play the entire story of ME3 with the same characters in a trio.
Just a crazy thought about how Mass Effect Multiplayer could work really well and be very interesting.
