I've read a Gameinfo (or something like that) and plenty of new characters show up. So just to be sure I'm not missing anything, I'll go over the list. Playable: Optimus Prime Megatron Grimlock Cliffjumper Jazz Starsceam Bruticus Bumblebee Vortex Most likely playable: Megaron Hopefully playable: Shockwave The rest of the Dinobots Laserbeak So, have I forgotten anyone?
Bumblebee is playable. The November issue of GameInformer (with the FOC cover story) outright says he's the first character you play as.
Confirmed to at least be in the game but unknown if they are playable or not are Megatron, Shockwave, Slag, Sludge, Snarl, & Swoop. Also Brawl, Onslaught, Swindle, Blastoff, & Metroplex. We've seen concept art for Wheeljack, Arcee, Perceptor, and depending on who you ask Sunstreaker. Also I can't imagine not being able to play as Megatron or Soundwave.