Beautiful graphics with consistent frame rate.
The graphics aren't great if you stand around and really examine them, but when you're whizzing by them at super sonic speeds, Sonic Generations can look really good. The frame rate doesn't drop when you're speeding past 100 things at once, and all the stages pay homage to the original stages from previous games. You'll recognize bumpers from Casino Night zone, bouncing mushrooms and levys from Mushroom Hill Zone.
Gameplay is simple, but fun.
The controls aren't drastically different then the console version. Run, jump, boost. Some features, like being able to customize both Sonic's with abilities and doing midair tricks to fill up the boost gauge are completely absent. That being said, playing as Classic Sonic will still feel like playing on the Sega Genesis, and nostalgia abounds. Playing as Modern Sonic is still a roller coaster ride where you feel the thrill of boosting through the stages at supersonic speeds.
I beat this game in a day. What I didn't like was that while there were three stages in the Genesis era, there were only two for the Dreamcast and Modern eras. It felt as if they weren't really putting a lot into this game, which is understandable, given this game was released shortly after the 3DS was launched. What made the game feel even more rushed was that the rival bosses, Metal Sonic, Shadow, and Silver, each had their battles on a stage in their era, rather then their own stage like in the console versions.
Missions feel useless
I did NOT feel like doing any of the missions the game unlocked as I played them, and neither did the game give me any incentive to. The replay value of this game, like the console version, comes from wanting to master each stage and get as high of a score as possible on each of them, rather then doing these missions.