The 15-second Rebels teaser that aired yesterday was probably someone's first look at the series. Previous announcements were made at Celebration and online, but this was the first Rebels spot on TV, paired with Mighty Med, a show aimed at young teen superhero fans. For some people, it probably felt like a first step into a larger world.
For Star Wars fans who have been watching for every bit of information dropped by Dave Filoni or Pablo Hidalgo, there wasn't much new information revealed about Rebels in the announcement, besides that the show exists and is coming in 2014. Lightsaber Rattling has an exhaustive shot-by-shot analysis of the spaceships shown, but the most interesting part for me is the voiceover suggesting that "The Jedi will rise."
That immediately makes me think that the show might involve new Jedi characters, or even Ahsoka, but it's still all rather unclear.
Rebels is also clearly continuing Disney's desire to tie their Star Wars more to the Original Trilogy than the prequels, with the animated teaser replicating the opening shot of A New Hope. In total, the teaser packed three ships into 15 seconds - giving just enough information to intrigue fans.