IGNPC: Is it centered on several planets or just Earth? What's so special about Earth anyway? Are humans part of the big war or just drawn into the fight?
Ted Morris: Just Earth for now - but as Adam mentioned, the war has been raging for centuries on a variety of planets. The full title of the game is "Universe at War: Earth Assault," and it is here that the various races collide - with humans caught squarely in the middle. In the grand scheme, Earth really isn't any more special than the other worlds that have been "harvested" by the Alien Hierarchy. What makes it special to us is that we live here! Humans can't even begin to compete on the level of destruction that occurs in the game. After being initially drawn into the fight, it becomes quickly obvious that humanity, as a race, is pretty much screwed. So, while humans do play a role in the game, most of the ones you see will be running for their lives. There are a few notable exceptions that play a critical role in the story campaign however.

Update: here is the official press release from SEGA announcing the game, which is set to ship later this year.