The modern games have their moments. Improvements such as the Homing Attack, better flying for Tails, and the Light Dash (especially the Light Dash) all do their part in improving the gameplay, and I think some of us will agree that some of those improvements would be interesting to say the least in the 2D games. Personally, I've resigned myself to the fact that I'm never getting a game as good as my beloved Sonic 2 ever again, so I just put up with what we have. If you ever saw my post a while back about what needs to be in the next Sonic game, you'll notice it's not about "going back to the classics", because that's an impossible dream. It's never going to happen, so I think what we have now should be improved. There are some things the modern games do right-probably the best example of that is a level such as Speed Highway or Final Rush-rather than tossing away that formula, we should break it down and see if we can make the good parts better and the bad parts nonexistent.
That said, note I mentioned "beloved Sonic 2". It's my favorite game by far, partly because I've been playing it since I was three. The classic games are better by far...but that's just it. They're classic. We're never going to get the past back, why do we keep trying?