As someone said, when people say "SONIC SUX", they are rarely referring to the character itself. I see no fundamental flaws in the Sonic the Hedgehog character, along with the cast of characters. When you get right down to it, it's your standard mix and match cast of the badass, the girlfriend, the sidekick, the semi bad person but who sometimes has good intentions, etc etc etc.
It's Sonic TEAM that is the problem here. To sum up Sonic team in one phrase, "TRYING TOO HARD". They try to give the Sonic games these epic stories and amazing scenery and try so hard, but the fact is that for a character who is a BLUE HEDGEHOG WHO RUNS FAST, none of that is necessary. "You put Sonic here, he must go there, GET GOING" is all the games really need, but Sonic Team forget that that is exactly what brought Sonic to the forefront in the first place.
I've always hoped that Sonic Team would get their heads in the game, but given the announcement recently of SONIC KART RACING, this is not going to happen anytime soon.