Thanks for your responses! That's interesting that there's a level up feature. And yes, that review from when Sonic and the Secret Rings first came out is very helpful.
I'm still on the fence about the Storybook games, but currently here are the games that based on what I've gathered I'd consider true 3D platformers in the Sonic series (some better than others, of course):
Sonic Jam (albeit on a much smaller scale)
Sonic Adventure
Sonic Adventure 2
Sonic Heroes
Shadow the Hedgehog
Sonic the Hedgehog (2006)
Sonic Unleashed
Sonic Colors
I've also excluded Sonic 3D Blast - it's funny how many times video game marketers have redefined "3D" in their solicits.
If anyone has any suggestions for the list, feel free to make them! And please continue to discuss the Secret Rings and the Black Knight, as my mind isn't made up completely.
Right now, I'm thinking when I get to that point chronologically in my gaming, I'll rent the games and see how they play first-hand.