So far it's been confirmed to be separate from the main story and include a competitive setting.
Originally Posted by ACt
I dunno... haven't read about it, but if they can make the game suitably difficult and you can get the entire team to carry out missions together (meaning having 9 players at a time), it could be good. I think the best thing they could do with this is have a similar level set up in co-op campaigns to the final mission in ME2 - multiple objectives so you actually have to break up teams to finish the level. But balancing that with a single player campaign is probably like having to make two games. So unlikely.
If it is just a co-op versus battle thing... then the only upside is Krogan death matches.
Multiplayer for the main Mass Effect storyline can seriously fuck off. Do not want.