In an interview with EW, Star Wars Rebels executive producer Simon Kinberg discusses various aspects of the new animated series. He's asked about specific characters (Darth Vader, The Emperor etc) and although he refuses to confirm or deny their presence, he does say that "the main characters are new characters". One thing Kinberg is happy to talk about is the tone of the show. It seems they'll be taking things back to A New Hope for the "intended voice" of the series, and although we can expect a fun adventure, it sounds as if they won't be afraid to get a bit grittier than the likes of The Clone Wars for example.
"The world we're creating is an Imperial world. You're seeing the impact of the Empire, of stormtroopers around the galaxy, abusing and oppressing people. Thematically and politically, it goes to some dark places. But for the tone of the show we took our cues from the original movies, which had fun and adventure and swashbuckling with emotion and grounded human characters. We took all our cues from the original films. Obviously there are slight tonal differences between New Hope, Empire and Jedi. But I think the closest intended voice of the show is A New Hope. So there are places where we get into darker backstories, there are places we see how cruel and malevolent the Empire can be, but for the most part it's a fun and character-driven story. Again taking our cues from the original films, it's less maybe political than the prequels and more personal. It starts with a few character introductions that will precede the show. I wrote the first two episodes, they're like a one-hour story across two episodes where we introduce the main characters in the show."
Sounds great to me. There's much more to the interview so be sure to click the link below to take a look.