I came here to see what was added in 2.1 since I never played any other version and found out you added ring physics.
You added one of the worst things to ever come out of Modern Sonic. As if Red Volcano and Egg Rock weren't hard enough, now taking hits means I'm less likely to get rings back. Wasn't this game aiming to be the classics brought into 3D properly (which it is, by the way)?
I just have a personal hatred towards ring physics. They make actually difficult Sonic games harder for all the wrong reasons. Other than that, this update is perfect.