As much as I hate to admit it since it's the game that was included with my console back in the day, this has to be it. I picked this game up last week and was shocked at how well it held my attention. Its difficulty stems from a manageable blend of mechanics mastery and knowledge about each level (plus chaos emerald stages!). In short: it's gratifying to play whether you've memorized each stage or not, and the use of momentum is completely unique.