Sonic 1, Sonic 2, Robocop Vs. Terminator, Streets of Rage, Golden Axe, Super Hang On, Revenge of Shinobi, Road Rash and a couple others.
Mega Drive (Model 2) is my favourite console of all time that I proudly own two of them, both complete in box with everything (the second one was given away for free by the seller).
I still wish I had my Megadrive too but thankfully most of the games I enjoyed on the console have been ported onto many devices now . Sonic being one of my favourite games of all time (1-3). Other games I enjoyed were Road Rash, Ecco the Dolphin and Golden Axe. I managed to get through quite a lot of Mega Drive games when I was younger