The characters and worlds are aggresively one-dimensional. The world being fractured is no excuse to only give everything a "fraction" of personality.
Some of the people on the show are trying to pass it off as canon to the games (They can say the games are canon to the show, sure, but they straight up do not have the authority to dictate the canon of the games) but I'm not buying it until someone from actual Sega says so, and not even Iizuka has said so despite outright stating he wants to "unify" the continuities. The writers clearly only have a basic idea of the Sonic setting, because they think everyone lives in Green Hill, that Eggman has never used robots without animals inside (nevermind the fact that he straight-up hasn't done it since Adventure 2), and that Chaos Emeralds are just randomly hidden in rocks that formed long before the last time the Emeralds scattered (though that one's more of a minor nitpick). There's also the obsession with chili dogs (a nod to chili dogs once or twice per game/show is charming. Constant reference is unfunny and out-of-character), or the fact they've once again reduced Amy to a one-note character that isn't even the correct note. Has no thoughts but her obsession with Sonic? Nah, done that. Bargain-bin Sally? No, the fans already forced Flynn to knock that off... This time, she loves nature! No, like, that's the main crux of her personality now, not just a little character trait. I'm sure she does havw a fondness for nature but I don't remember her going off about trees and flowers and stuff in any of the games... I guess her boundless compassion, that literally gave a robot free will and helped Shadow unlock his real memories of Maria's last wish, isn't really special at all, because as we all know, female characters being "emotional" in any way is offensive and stereotyping, which is why making her obsessed with flowers out of nowhere is totally better.
Lastly, the flashback to the time Sonic first met Knuckles is just straight-up wrong, I won't even get into any inaccuracies besides the fact that Hidden Palace Zone is not even close to their first meeting, and they'd know this if they played the games - you literally see Knuckles right at the beginning of Sonic 3 before the opening stage even starts, and he appears to trigger traps and such multiple times throughout Sonic's story before you ever get to Hidden Palace Zone. Maybe you could throw them a bone and say that was the first time they were face to face for long enough to really talk, but the way it's framed still leads you to believe this is genuinely their first encounter.
Overall, I had to force myself through most of the show... Only partway into the pirate episodes did it finally become enjoyable to me, and "it gets good near the end" isn't really a good verdict.