I would be surprised if it was a huge jump across what they did conceptually in Unleashed. Even in the case of Colors for many accounts, most of the levels were the exact same and had nothing outside of like... Water to distinguish them with one another.
Sonic Adventure 1 and 2 are very underrated in this aspect, where most levels felt completely different. Even some of the newer games like many of the newer "Better" titles like the portable games and Sonic the Hedgehog 4's gimmicks were really forced, playing cards for backgrounds in Sonic levels just feels so wrong for some reason, but they went nuts with it.
That is not to say that conceptually Sonic Generations is worse. I think basic Sonic games more around cinematic values is cool too. It is just a different design mentality.