People must have more sensitive ears than I do. Bubsy only sounds slightly different to me, and SFII... well okay, its been years since I've played the SNES versions, but it doesn't sound noticably worse than the Saturn or PS2 versions to me.
There were, IMO, a few games that sounded better on Genesis. Aero the Acrobat for one (though this mainly because some levels had different music between versions, and I felt the Genesis was more appropriate).