I like Sonic, and 70% seems generous. Most with mass appeal, that is, no ingredients that would turn off anybody, are Genesis titles. My favorite non-Genesis title, Sonic Adventure, is still a massively flawed game that I would only recommend with caveats. And that's the high point of 3D Sonic gaming. Sure, other games do other aspects well, like Unleashed introducing Boost, but also chuck problems at you like unskippable half hour werehog stages and QTE. Gens finally gave us a pack of speedy levels with no gimmicks, but with Heroes style roller blade control. Frontiers let you adjust your own controls, but lacked focus and looks like a messy pop-in fest.
Sonic ends up being a mixed bad of shit and disparate good ideas that I wish they would combine into one game already. I think the main feature of a Sonic game is actually controlling/being Sonic (ever since Sonic 1) so if they mess up the way it feels to control him with an analog stick, they can add the best level designs and graphics we always dreamed of on top of that even for a third Gens expansion, it will still be a meh Sonic game to me. He's supposed to have feet, they nailed it in the first 3D game already, so my standards are set.
After playing six Shadow acts, I was "entertained" but my primal Sonic itch wasn't scratched. I switched to SA and blew through all ten levels in about 40 minutes, and felt better.