I see your point, but I have to side with the public opinion on the Classic games. They have great controls, awesome and iconic physics, great graphics and sound, as well as excellent level design. This especially goes for S3&K and Mania.
I love Sonic Adventure, but mostly because of, 1) its soundtrack, and 2) it was probably the most 2D-feeling 3D Sonic game we ever got. It was fresh and new, yet still brought back memories of the originals. Its level design was based around going fast, but it let you roam free most of the time and explore your surroundings; and be rewarded for it.
I don't really like SA2 because of this and other reasons. Most of the Sonic/Shadow stages are incredibly linear and lack a sense of exploration (except for Final Rush), Tails/Eggman's stages are neutered with clunky controls and cheap enemy placement, especially Tails' stages, and Knuckles/Rouge's stages have been made longer and more frustrating with the new radar and the maps being
enormous compared to SA1's.
I liked Knuckles' explorative stages in SA1, for the stages being fairly easy to navigate through (except you Sky Deck), yet making it challenging to get the Emerald piece. I also liked the idea of characters traveling through other characters' stages; for example, Sonic could race through the end of Speed Highway, then Knuckles could go through and, using his extra abilities, uncover hidden secrets that Sonic could remember to pick up next time going through. But yeah, both of these things are absent in SA2.
I did like Generations, as well as Unleashed, from what I've played of it (Wii version, and first level of PS3 version before I gave it away

), but they all don't bring the same magic that SA1 had. If Sonic Team made a new 3D Sonic game like SA1, with explorative level design and free-roaming aspects (and Chao of course), I'd probably get it. But as it stands, I probably won't get Forces. It looks cool, but it's obviously not gonna get good reviews from IGN, GameSpot, or any "professional" game reviewers.