It takes place in a time where the Empire is securing its grip on the galaxy and hunting down the last of the Jedi Knights as a fledgling rebellion against the Empire is taking shape.The series is being heavily influenced by the aesthetic of Ralph McQuarrie's concept art for the original trilogy - Which I think is an excellent decision; I really like that look! The logo above, and the following images were released by StarWars.com, as you can see, they really capture the crisp clean and bright look of McQuarrie's art:
The central ship in the above image is the hero ship of the series, the Ghost. TheForce.net uncovered a schematic of the ship, from a url hidden on badges given away at the convention:
Hoth Bricks posted photos from the Rebels presentation at the convention, there are a few highlights after the jump, but you can see lots more of the Ghost, new stormtroopers, droids, and location designs on Hoth Bricks: