Close to perfect (basically no complaints, no bugs):
Sega Genesis: NHL '94, Sonic 2
Atari 5200: Star Raiders
Atari 7800: Joust
Colecovision: Super DK Jr, H.E.R.O., Galaxian
Atari computers: River Raid, Frogger 2
Commodore 64: Raid Over Moscow, Maniac Mansion