Sonic CD was rebuilt from the ground up and the guy who led the development was just a guy who makes Sonic Hacks in his free time but when he displayed the game working on a iphone (or pad I forget) it caught sega's attention. It plays wonderfully and smoothly and even has both the US and JP soundtracks yay!

*now has retro sonic fix*

http://toucharcade.com/2009/07/29/christian-whitehead-on-sonic-cd-and-his-retro-engine/