The online multiplayer options are in the form of stage battles with two of you controlling opposing armies. So if you do like this part of the game, then the wide variety of extra soldier types on offer as you control the evil armies too should keep you happy. It all runs smoothly too.
If you chose to ignore most of the side-missions of the main game there is only about six hours worth of game here. But the laughs and tearing around the mental landscapes and scooping up the collectables should keep you entertained afterwards especially with such a killer soundtrack.