I just don't get it. I've never played a Sonic game I didn't like, and I've played '06. I'm pretty sure I've played all the 3D Sonic fames except Zero Gravity, and I can safely say I enjoyed all of them.
Don't get me wrong, as a fan, I enjoy whatever Sonic game I can get my hands on. However, personal prefenence about that game can possibly drive how they feel about it. Some people can hate 2006 because, let's face it, it was really bad. Then again, people outright hate it, while those may have some liking to it.
And to the average person/gamer, the Sonic series is a piece of trash because of how the media portrays the series now. I'm sure they pine for the classics and how Sonic sucks right after them. Sonic Team is actively trying to regain its strained touch with the fans, and if Generations and Sonic 4: Episode 2 is anything to go by soon, making Sonic relevant again will get it some proper recognition, but it will take some time.