Geeeeeee, I am not too sure how to respond this. But I could give out some examples like:

Warehog Stages: In Sonic Unleashed, perhaps it's the only way to make the game feel longer, like whoa dude! On my first play though, it lasted 10x longer than daytime stages. Plus add that lame battle music.

Too Fast in Production: Isn't it obvious? Every year we see Sonic in an all new adventure. He could use a break.

Not Sticking to it's ORIGINALITY: Sonic should be the way it is. And well he should stay that way since in the first game

Meh, stupid I know, but that's exactly what I wanted to say.