No, Sonic has had side quests since the chaos emeralds. It's only the indivdual levels you're supposed to beat as fast as possible. A whole game without sidequests that you can finish in one day is a waste of money.
But isn't that what some Sonic fans want but SEGA refuse to listen because they want to make the games longer with gimmicks, such as the Werehog levels in Sonic Unleashed, and then listen to that fanbase with Sonic 4, which has only 4 zones?