Fun, innovative concept. I thought forcing the player to collect 100% of the stars was a little tough, though -- maybe 80% would make it more approachable?
Very fun and polished game. Achievements are great; differing goals such as speed vs stunts add new dimensions to the game. Large number of characters is a good touch. I just wish character stats (speed/stunts/spin) were available within the game instead of only in the guide. 5/5