There are some things I loved about this show, and some things I definitely didn't. Here's my personal list of pros and cons.
(TL;DR: Pros: animation, characters, new story perspective, non-Autobot main characters, portrayal of Decepticons, Starscream & Megatron. Cons: Mid-show tonal shift, season finale, main villain, OP's face, Frenzy's design, Nightshade’s portrayal.)
Pros:
The animation was gorgeous! So fluid, colourful, and expressive- it's fun to watch.
The characters: I found myself invested with the characters, both Transformers and humans, which isn't something that happens often. I actually found myself caring what happened to them. The last time that happened was TFP.
I liked that EarthSpark moved away from the traditional heroic Autobots versus dastardly Decepticons! story. There's nothing wrong with that story, or else it wouldn't have been reused so many times over. But I really enjoyed that we were able to see the Cybertronians post-war, and how many of them moved on, as well as those that weren't able too. It was a pleasantly creative twist to have main characters that aren't Autobot or Decepticon, and to explore how they see the war from an outsider's perspective.
Okay, I know pretty much no one liked there being a human villain. But. By shifting the villainous focus away from the Decepticons, it allowed for them to be portrayed in a less 'pure evil by default' way. The war is over; we're allowed to see them as characters now, not just bad guys to knock down. I absolutely loved the episodes featuring Tarantulas and Starscream. Which brings me to my next point:
Starscream. Do I need to say anything? Bringing back Steve Blum was an amazing decision. That man is both talented and iconic. I was worried that I would constantly be thinking of TFP Starscream and be subconsciously projecting that existing character onto this one, but surprisingly, that didn't happen. ES Starscream was so unique that I never accidentally associated him with another version of the character. Now, I've never seen Armada, but I found myself really liking this sympathetic outlook on Starscream's character. I particularly enjoyed his dynamic with Hashtag and his conflict with Megatron, which adds a lot of welcome depth to, what is quite possibly my favourite version of the Starscream (perhaps after TFP)
Megatron's role in this show. I really liked how, even with his redemption, he and Optimus still have ideological disagreements, and they address how not everyone can forgive him after the things he's done. While I like and sympathize with this version of the character, I don't think he's quite entitled to that forgiveness from everyone, something the show seems to understand. (Also, I quite like Dorothy)
Cons:
There was a big tonal shift in the last batch of episodes, and the season finale... left a lot to be desired. I did like the Decepticons joining the fight at the end, but that's it. I definitely won't be rewatching those episodes.
The human villain, Mandroid was... where do I begin? I really hated him. I love to hate a good villain, but I just hated every second he was on screen. He's just so unbearably obnoxious, and his final design was creepy, but not in a good way. They tried to build up some character depth with him in the first batch of episodes, but just completely gave up on that thread and made him spiral. I just didn't like him.
Ahem.. Optimus Prime's face. Enough said.
Frenzy's design was... interesting.
Nightshade was kind of forcefully shoved in our faces..
(I was going to complain that there wasn't enough of Starscream, but honestly, I'm just grateful he got as important of a role as he did in episode 21)
In short, there were more positives than negatives. (though I passionately dislike the negatives)
EarthSpark is a good show that I enjoyed and that I think a lot of other people did too.