Spark of Rebellion, as the preview above lays out, introduces the show's various characters, including protagonist Ezra Bridger (Taylor Gray), a young orphan who's managed to scrape by thanks in no small part to his unrefined ability to use the Force.
The clip below, "Generations", teases the trouble that follows Ezra after the events in Spark of Rebellion, when he hooks up with a ragtag group of rebels in the making - including, Kanan (Freddie Prince Jr.), a Jedi-in-hiding who has been passing himself off as a smuggler. As for Rebels' central antagonist, The Inquisitor (Jason Isaacs), he remains something of an enigma - one who is fairly handy with a lightsaber (...or two), though.
It's interesting to note that multiple Rebels trailers have now highlighted a special appearance by Obi-Wan Kenobi (via recorded hologram), and shown that he, in part, inspires Ezra and his comrades to take up arms against the Galactic Empire.
There are rumors of an Obi-Wan Kenobi spinoff film being in the works, so if true then this could be another way that Rebels connects to the larger Star Wars universe of the past and future... Or it could just be a cameo by a fan-favorite character and not much else. We'll see.
Regardless, the bigger issue is whether Rebels can follow in the footsteps of its predecessor, the Star Wars: Clone Wars animated series, and in time evolve beyond being a kid-friendly cartoon adventure (which, on its own, is not inherently a bad thing either). Rebels TV show co-creator Simon Kinberg has indicated that is, in fact, the plan - for Rebels to eventually touch upon the darker and more complicated realities of life under the Empire's rule - so that's encouraging.
Star Wars Rebels premieres with Star Wars Rebels: Spark of Rebellion on Disney XD on October 3rd, 2014. It begins its regular series run a week and a half later on October 13th at 9 p.m. ET.