So I want to love Sonic. I feel like someone else said - the games want me to go fast and punish me for going fast. They're called platformers, but they don't feel like platformers to me, the jumping has always felt bad, and the way that inclines in the 2D games punish you for jumping on them was a thing I never quite got the physics of, and found them really frustrating.
I think the later games have built so much on top of these foundations that they're weirdly inaccessible to newbs, despite being very "railsy, play themselves" feeling.
But I'm gonna get roasted and say that I think Sonic is a great franchise. He some how managed to emerge from the 'tude era of mascot platformers, personality intact, and emerge from the fall of Sega without becoming a clone of some other game. Mario has defined the platformer, but Sonic continues to exist, doing something different, as the Loyal Opposition, and that's good for fans and for the industry.
Mario is "Bowser of the week vs everyman". Sonic is "superhero soap opera"
Mario is "jump", Sonic is "run".
Mario is "build momentum", Sonic is "dodge".
Mario is your avatar in the game, and when Mario jumps you make him jump.
Sonic is your ally in the game, he goes fast on his own, you are his eye in the sky, telling him the safe path.
This is a mindset change I never quite mastered when playing the games, and the game's own inability to know when to cater to Sonic fans and when to bring new fans in leaves some muddled design - that's part of why he's always been so contentious. But watching my partner play (she loves Sonic), has sorta taught me how to enjoy it, and every now and then it will click and I'll get it.
Also, even the bad music in Sonic games slaps