I remember Sonic Adventure used to confuse me as well.
Sure it keeps asking me to reassess which direction to hold to make Sonic go forward, but I usually seem to pick the right one. It's a great idea I reckon, and really well implemented. The Sonic games started playing with the camera like this back in Sonic Unleashed, I think, seamlessly switching perspective to incorporate sections of 2D gameplay into 3D levels. Hang on, the level's gone side-view all of a sudden. There's Sonic Adventure-style grinding as well, even though Sonic left his Soap shoes behind a long time ago.
