The E3 announcement featured a very short teaser video, in which an unknown individual is shown from a first-person perspective walking across a snow-covered landscape. He looks up as a laser blast hits the ground to see a snowspeeder spiraling toward the ground ahead of him. Overhead, the foot of an AT-AT lands directly in front of him, as the trailer ends with the Battlefront logo.
Here's the half-minute trailer:
While it's unclear how long EA has been working on this game, the fact that the trailer was this short suggests that DICE is not very far into the development process.
No additional details about the game were announced at the press conference. A post on The Official Star Wars Blog promised that "platform and release information will be revealed at a later date."
One interesting fact that we do know about this game is that, as of right now at least, it won't be a numbered installment in the Battlefront series. Lucasfilm's blog post said that the game is "currently titled Star Wars: Battlefront." Given the inclusion of Hoth gameplay, it's likely that this won't be a "third Battlefront," a.k.a. a new installment in the series that began under Pandemic Studios, as some have been expecting since BFIII rumors began circulating.
Instead, this seems to be a "reboot" of the Battlefront series, with new gaming experiences and better graphics but familiar and well-traversed locales. Given how much ground the first two flagship Battlefront titles covered, it probably wouldn't have made sense to develop a direct successor to Battlefront II anyway. That being said, there will almost certainly be at least a few new maps in addition to the popular Tatooine, Hoth, and Endor settings.