One thing that Rebels did that I liked was it brought Vader back just a little from the Twilight tinged emo child that EU and RotS had turned him into. It's one thing conflicted about your emotions of corrupting the child you had with the wife you thought you killed, but when the EU literally had Vader literally kill Darth Maul through the power of self-loathing, you have something less than a Sith Lord and more somebody who sits crying in his meditation chamber (oh wait somebody made a picture of that).
Rebels at least brings back a sense of that power of the Dark Side that the Emperor gloated about. The anger that had him gloating that his former master was too weak to pose a threat to him before trying to slice him in half without a second thought. No time spent afterward remembering all the good times that Obi Wan and he had together, just getting ready to fly out to shoot a few X-Wings.
On the downside, Rebels seemed to have really downplayed the significance of Star Destroyers. The SD was the first image you saw of the Empire's might as it dwarfed the Tantive V over Tatooine (spoilers?). In Rebels, I don't think I've ever seen one fire a shot even when a cruiser that they know is carrying rebels and a Jedi is trying to escape from it. They just hang out in the atmosphere of Lothal with spotlights shining down as if they're mile long police helicopters. And if a handful of malcontents manage to make it inside, just write off the whole ship and crew.
Lieutenant: Sir, a transport matching the description of the one that blasted out of Lothal has just entered the system and is heading straight towards us.
Captain: They're moving to attack position. Shields up! They can't repel firepower of this magnitude!
Lieutenant: They actually just docked in the main hanger bay. Stormtroopers report 5 rebels and a droid disembarking.
Captain: FFFFFFFUUUUUUUU!
