Well i've just seen Youtube clips (will buy the platinum edition) but the classic treatment for the modern stages has been really exciting.
I've only checked about 4 stages (don't want to ruin the entire experience).
The stage that blew me away was Crisis City shockingly, the classic treatment was more true to the actual stage than the modern treatment which actually destroyed a level from Sonic 06 (bet you never heard anybody could say that).
See for yourself:
EDIT: The [video] tag wasn't working for me.
The Original featuring 4 acts of Awesomeness:
Act 1: Skate Board
Act 2: Rail/Platforming
Act 3: Platforming
Act 4: Mach Speed
P.S. Even though he got an S, he was still a sucky player. He played really safe and missed all the cool/risky shortcuts.
Then we have the classical and re-imagining of Generations.
Both versions could've been better but atleast the classic one tries to be faithful.
Another thing that bothers me is the weird Marioish stomping thing they've got Sonic doing (since Unleashed) instead of the bounce he's been doing Since Sonic 3 (the bounce was omitted in Sonic Adventure & Heroes as well). Lastly I hate those red coins, whatever happened to the emblems we used to collect.
Other than minor nit picks Generations does seem to hit the right notes, where as Colors was over rated.