Thinking harder about it, and I know another big reason why I really dont care much for Sonic anymore, to the point of not even buying the games used. Sonic is the type of series that I can play on autopilot. It's gotten boring as of late because I've been playing it as long as I can remember, and it has refused to grow up. This has little to do with the game being good or bad, because I feel the same way for Mario. The entire NSMB series felt boring to me. On the other hand, I adore Galaxy and SM3D world is probably the most fun i've had with a platformer in years.
Of course Sonic isn't this way from lack of trying, and this is why Heroes/Unleashed are the 3D sonic game I respect the most, while Colors/Lost World felt like it was picking on me with the way it was designed. I think most of Sonic's shortcomings are just from a multitude of development problems -- you can point out whats physically wrong with the games all day and night, but the truth is those problems could arise from any deeper issue, and since the shortcomings have been so consistent and so thorough i can only assume it's deep rooted enough in Sega to not change anytime soon.