An excerpt from GamePro's massive preview of :

The most interesting part of Revenge of the Fallen will undoubtedly be the online multiplayer mode, which will let Autobots and Decepticons fight out their aggression in robot-on-robot super violence. Players will be able to align themselves with the faction of their choice, and take their robot of preference online in team matches, capture-the-flag events, and of course, deathmatch modes. More characters from the Transformers series will be available in the multiplayer setup, while custom skins gathered in the offline story mode challenges will help players distinguish between their Decepticon Seekers more easily.