"Hardcore" Sonic fans hate almost every Sonic game for 1 reason or another. I honestly don't get why they set such high standards for the series myself. Sure the games may have 1 issue or another that no one can deny, but personally I think the overall negativity is blown out of proportion. I mean really, what's the point of just making them all like Mania? Is that really what said fans want? I think it'd get boring after awhile myself if it was the same game with just different stages and stuff. I didn't think Dark Brotherhood was bad, I didn't think Forces was bad, and the only games I really didn't care for playing were the ones that needed the Wii Remote (wasn't a fan of using that thing). I haven't played every Sonic game in existance, but I have played most of them. I might just be more open-minded and less high-standardish than others but still...
P.S. From all these posts I'm starting to think people want to see Knuckles in the game... But that's just crazy. I mean it's like they expect to find the Master Emerald in The Churning Mists...