Presentation wise: Taking it's backstory seriously enough to add a crap load of characters, while in the same swoop destroying it by 1) just throwing darts at a wall of ideas or whatever they could interpret from an executive's doodle on a wet bar napkin 2) pandering to the furry set that has latched onto the franchise.

Gameplay wise: Forgot the entire thing was about the choice between platforming carefully and exploring or platforming incredibly fast and looking for ways to collect "enough" coins while finding ways of going even faster. Both styles had a risk and reward system that didn't punish you for doing one over the other. I've yet to play a non-2D Sonic that does this well. SA1 and 2 get a nod though, because fuck, at least those tried.