I'm Tired of Pretending It's Not - Sonic Adventure and Sonic Adventure 2 Battle

I would add in sonic heroes to this list as well, but still, SA2 Battle is still by far the best representation for a sonic 3d game.

It has speed, it has good level design, it has good platforming. It has alternate routes and secrets.

Pretty much every 3d game since heroes has missed 1 or more of these things.