I thought Sonic Advance 1 was good in a Sonic & Knuckles way. Its platforming isn't the best (even when setting aside my want for speed), but it's jam-packed with atmosphere.

I should have mentioned this before, but Sonic and the Secret Rings is a real shoe with a learning curve beyond the player's control. As you play, you earn moves, which work like the badges in Paper Mario. These extra moves make the game easier, so going back and playing an earlier stage once you have a new item will make it easier to get a gold medal in. It won't be easier because you've played the game more and you are better at it, but it'll be easier because the game lowered its difficulty a notch by giving you this ability you didn't have before.
I'm fine with that in adventure games--shoe, it's the heart of adventure games. I can even tolerate it in Sonic Adventure 1 because it's trying to be an adventure game. But putting such tricks in an otherwise no-thought-required speedy platformer is just a dirty trick.

There are a few other unsettling things about Secret Rings as well, such as the extreme difficulty of some of the missions--it's hard enough to complete such missions at all, let alone get a gold medal in them. Then again, I find SA2 extremely hard and somewhat unfair to get A's in.

As I understand SatSR is a real love it or hate it game, though.