My history with the Sonic series is quite a rocky one. I could probably be called a fan with the amount of titles I have finished, but at this point I have gotten a big amount of dislike for most of them. Replaying Sonic games have the opposite intended effect on me, the more I replay one of the Genesis games for example, the more flaws I find with its design, to the point that games that I originally thought were at least just ok or janky with a couple of moments that they do slightly well, turn to bad or terrible. And there are of course games in the series that are just bad from the get go.
I don't like the original trilogy, CD is ok at best and who the fuck designed Wacky Workbench at worst. Adventure is bad in a fun way, and 2 is bad and boring (Adventure 2 is a game I never liked to begin with). Unleashed has a good setting stuck in a mess of a game, be it the HD or SD version. Only the first Advance game in that trilogy is fine, Rush exists but has a banger soundtrack, Lost World is definitely in terms of concept what if we gave 3D World's core creativity to people that don't know what they are doing, Generations is held back by its terrible missions and the last level and boss fight leaving a sour note. Heroes was a thing, make the game increasingly annoying with each playthrough, etc.
At this point the only stuff I still hold on a positive note are Colors and Mania, which both I haven't replayed in a while and I kind of not want to, they'll remain in my memory as solid, 7/10 games. Black Knight is in a weird spot where the gameplay is nothing good really, but is not bad enough for me to despise it, and it has the only Sonic story I can respect.
Why did I stick with the series for so long one might ask, well, they aren't too painful to finish, lot of them are pretty short, music (most of the time) is good, and they do a couple of things here and there slightly well to call charming.
Forces was kind of a breaking point, is the lowest I have played from the franchise, couldn't even finish it, a somehow boring story with 0 personality, awful music, worse controls and level design than usual, and still, since Generations, somehow having the game look worse than Unleashed and Colors. just a soulless game. And then Colors Ultimate, why would you ruin that game, and again the music, they are awful at managing any sort of electronic instrumentation, is excessive and annoying, just the Planet Wisp remix was enough for me to not get the game.
Not excited about Frontiers at all, or new Sonic things in general, didn't even like the first movie, I'm just kind of done with the franchise.
So no, I don't think is a great franchise, it was a sporadically interesting one.