Sonic & Knuckles (Megadrive)

Sonic & Knuckles was most probably the final proper Sonic game Sega released; at least until the forthcoming Sonic 4 hits consoles worldwide. It was released back in 1994 and was a direct and definitely worthy sequel to Sonic 3, that featured the rather smart lock-on technology. Happily, you can still grab a cartridge with the Japanese MD version of the game (it will only run on a Japanese MegaDrive) via Play Asia.