FYI:
Sonic 3 Complete (as well as many other SEGA Genesis / Mega Drive ROM Hacks) can now be downloaded and played legally via the Steam Workshop, as long as you already bought Sonic 3 & Knuckles (or any other available Genesis / Mega Drive game) on Steam:
S3&K =
http://steamcommunity.com/app/34270
S3C =
http://steamcommunity.com/sharedfile.../?id=674578957