Alright. now since Sonic Generations will be released very soon. There is only one MAJOR thing to think about.... D. L. C. (Down-Loadable Content).
Now this is something to really think about because DLC is a big thing. Could it be SKINS, characters, music, epilogues, Extra stages, co-op levels, Zombie levels, etc.
Now those things are something that I would want but the question is: "What do you want?"