Well, yesterday I got 100% on this game and got S ranks on all the missions (gloat gloat gloat). And that being said, I believe this was one of the easiest Sonic games out there as this is the first time I've ever been able to do this on a Sonic game.
Overall I think the game was pretty good (I played the Wii version, FTR). The day stages were the absolute best, even though steering was rather difficult. The werehog levels were okay, but I wasn't very keen on the fighting system. I used the classic controller, so mostly I was alternating between X and Y and sometimes I didn't get the combo I was trying to get. Also, there should have been a way to turn off "Super Werehog" (or whatever they call when you transform after filling up the bottom gauge).