So...I beat Sonic Advance 2 SP. At least, the Sonic part. Haven't tried the other characters yet. Overall it's...still pretty rough. I like it on the whole, once you get into a good flow in the levels there's nothing quite like it...but goddamn those bosses, man. They're interesting in concept but in execution holy hell are they the most frustrating things in the world. The SP Ring system is still kinda stupid no matter what you do, too. Certainly SP makes it easier by adding more and reducing the requirement from all 7 to 5...but that's still pretty steep for a game that pretty much actively discourages slowing down and exploring
I like it, just don't know if I'm going to ever play the bosses again, at least