There was also generations.
Generations was kind of a disappointment to be honest, and the 3DS version was better than the console/pc version, so that's saying a lot.
With the 3DS version at least with online vs you had a reason to go back and replay it, specially since you needed a fuck-ton of points to get the highest rank on your card after you S-Ranked all the single player stages and cleared all the Missions you could unlock via street pass. it was fun battling other people, especialy if you were in a situation where both players are so good, you're practically neck and neck (you could actually see their shadow in the same screen). Finding all the shortcuts were fun as well. Also the 3DS version has Big Arms... nuff said.
On the console/pc versions, yea the stages themselves are better, but once you unlocked everything, what was left? Speedruns you can post online to see how you stack up with other people? Great, so a mode specifically for hardcores/trannies.
Even in Sonic3K, (and of course Mania) after you beat the game once, you had a bunch more save slots for other games so you could do it again with other characters. Don't want to get all the emeralds this time? Go for it. Want the best ending with Tails to see his super flickies help you? Knock yourself out. Want to play Knuckles & Knuckles on Mania? Enjoy.
