I also just finished Rebels. To frame this, I did use a watch guide which dissuaded me from a number of poorly written or executed episodes (I tried to watch one of the not-recommended ones and it was... p bad to say the least).
Rebels has a lot more fan service and too-obvious tropes, but it also has some surprisingly deep moments and the inclusion of seen-before villains and allies is actually a mostly welcome occurrence. I would say on an episode-for-episode average you can expect an average to above-average level of writing and execution, but individually the highs are high and the lows are low.
The main cast is mixed imo, Kanan is my personal fav because he's limited by his admittedly incomplete training and exile BUT without being a hopeless incompetent. Also he maintains his jedi-ness without succumbing to and in the end overcoming the shortfallings of the order. As for the others,
Ezra is a hit or miss for me, in the beginning his struggles are compelling as a makeshift padawan who doesnt really have a hope in defeating the empire, as his powers and plot-armor grow he becomes steadily less interesting until he's capable of effecting the universe more than he ought to be. Maul (who is interesting by himself) and good ole Palpatine seem to think he's really important for some reason (even though he really isnt) and its a bit jarring.
Zeb, Sabine, and Hera all have their moments, but like @itsnotlogical pointed out they more often resort to their NPC energy and fill their little archetypes (which can be visibly apparent at times, especially with Zeb). Chop is chop... who knew giving R2D2 arms would be so successful lol.
Callus is fun, but he becomes a spy a little too easily for my liking lol.
Thrawn got butchered, a big waste as many before me have pointed out.
The rest of the (mostly Imperial) rogue's gallery don't really get enough screen time to warrant attention (even Vader is p meh after his initial hunt for Kana and Ezra).
Special treats like Rex and Kenobi are great!
In short, while they the design and writing teams were (thankfully and with appreciation) doing a great job paying homage to the universe as collectively imagined, they also fell prey to Disney's, "just make it different, not better" syndrome. I am unsure why (other than being controlled by a creatively-incompetent corporation like Disney) artists, writers, and creatives in general struggle to write compelling stories in the SW universe, before Mandalorian (which I thought mostly nailed it), a good New Star Wars story looked like Star Wars, but was dreadfully boring, and a bad New Star Wars story looked like generic sci-fi rip offs of Star Wars with stories that LITERALLY didn't make any sense or had so many plot holes you were at risk of breaking you neck navigating them.
Compared to those, Rebels rates fairly high. (but like Clone Wars, is too painfully close to greatness to enjoy it again without wondering what could have been)