I'll just give a brief outline here of what's known about MP so far...
MP will include the usual vanilla game modes:
Capture The Flag
According to an article at IGN, there might be a couple of other modes available - but there are no details, and this could be unsubstantiated rumour.
The game will support up to 16 players online (including via Xbox Live).
You can play as Republic commandos or 'other' characters.
There are no co-op modes in the game.
There will be 'downloadable content' after release
There will be 'Matchmaking' via Gamespy [arcade]
And that's about it.
Personally, I was hoping for a squad-based MP mode. I know others would have liked to see a co-op mode for SP (considering it's a squad-based shooter). I know there are sometimes issues around getting co-op to work properly in story-driven SP campaigns, so I can understand the ommission there. However, I would have expected an MP game mode that focuses on the 'squad-based' aspect of the game.
Team Deathmatch can be fun - but it's not exactly innovative. Capture The Flag will probably be more popular, and is at least a better team-based game.
I just can't help thinking there's something lacking. An objective-based squad-based team MP mode where you have to complete a certain standalone mission would have been appreciated. Maybe something like this is planned - but as stated above, the only officially confirmed modes are vanilla MP.
I can see that something in the Counter-Strike style would fit well with this game. Considering the SP missions will include assassinations, gathering intelligence, destroying objectives, etc., the MP side of things really cries out for game modes along those lines.
I'd be interested to hear anyone else's thoughts on this.