The Sonic generations physics weren't perfect, actually they felt scripted in a lot of instances. Such as it wasn't your speed that determined your trajectory and velocity once leaving a ramp, it was the ramp itself.
To put it simply, Sonic on the genesis designed the stages around the physics. Sonic generations designed the physics around the stages. Not a bad thing in itself as they still managed to make an excellent and entertaining game, albeit one that seems to lack in some gameplay opportunities presented in the genesis originals.
But hey, so long as Sonic 4 Ep 2 doesn't use the
Sonic Rush physics engine, whilst attempting to design genesis era stages (to the best capacity DIMPS has to offer), we're good.
I've been hearing DIMPS doesn't even have any part of S4EP2 now, thank god if that's true.