Sonic The Hedgehog 1 (Sega Master System) - FM hack by ValleyBell
ValleyBell, an amazing hacker / programmer / musician, decided to completely overhaul the soundtrack of the first Sonic game for the Sega Master System, redoing all the songs (and adding some Easter eggs in the process, too) to take advantage of the YM2413 sound chip, which was included only in certain Japanese consoles. This hack, other than on emulators, obviously, is thus only playable on the appropriate hardware, but there are several means to add a YM2413 to your Master System and/or to your Mega Drive / Genesis.
I didn't want to spoil the Easter eggs, but I couldn't avoid at least one to end up in this video: if one beats the game with all the Chaos Emeralds, Marble Zone's music plays instead of the ending credits song (yes, in case you didn't know, Marble Zone was meant to be included in the 8-bit version of Sonic 1 just like it was in its 16-bit counterpart).
You can see the official release topic here: http://sonicresearch.org/forums/index...
And the usual resource for the Sega 8-bit world is smspower, of course: http://www.smspower.org/
Enjoy :)