I watched all three. I thought the first one was a pretty weak start. The first half suffered, surprisingly, from Oscar Isaac's voice acting. He sounded kind of bored? I really have no idea why he decided to recruit some flailing limbed jittery guy he just met as a spy, or why he had him go undercover as a mechanic when Kaz has no mechanical experience. But I guess making terrible decisions is in character for Poe. Then the second half of the episode had a LOT of Kaz walking around trying to find items and being introduced to new characters. It went on too long. The race part was good.
I liked the pirate fight in episode three. Episode four...well, I guess it had some character development for Kaz.
The animation looked very good in the action scenes. Sometimes when they were standing around talking it looked too much like an RPG. I liked the variety of character designs and alien species seen and the spaceships.
I wonder if Leia originally had dialogue in the first episode and they cut it because of the voice actress getting into trouble.
So yeah I know I wasn't crazy about Rebels when it first started either and it got good, I just with there was more than grabbed me from the start in this.