I assume this game is set at some point during "The Great War" that first pits the Autobots against the Decepticons in a long lasting civil war that eventually reaches Earth as indicated in the various cartoons, comics and movies. Also the official website, TransformersGames.com, has been updated to reflect the new game with a countdown clock in the Cybertronian language and a link to sign up for "future transmissions."
The game's release date is to be determined, the platforms are PS3, XBox 360, and PC. Below is the video or click here for the embiggened version.
Update: Click here for nearly a frame by frame gallary of images from the trailer.