the differences are... well, I'll try to be neutral. So the OTG system is different, GG has a weight system, FRC's, pin point precise timing, spacing based combos (ie if your attack is off by a frame, you messed up the combo; hyperbole), and generally the untechable frames are longer, damage that averages out to around 60% for the cast, dust, no ground techs, and a lot more options/combos for 1 situation, I could go on.
Basically BB is more forgiving but is less.... satisfying I guess?
but if you're transitioning from BB to GG... basically get faster at everything you did, faster hit confirm, faster combos, etc.
Finally I disagree on the character design part, but that's generational dissonance.