I'm actually very disappointed in the game - because it was not a Sonic rip-off of Super Mario Galaxy.
Just think of Sonic spindashing around a miniature planet and jumping off when reacing top-speed - he'd orbit the planet at least once or twice before coming down. That was the best part of Super Mario Galaxy, and it would've made so much sense with Sonic!
...Instead I kept wondering why Sonic can fall down (or up, respectively) off a "tube" when he can also walk upside down on it. -_-;;