Here is a list of a few games that I practically liked on the megadrive.
Altered Beast Alex Kidd In The Enchanted Castle The Adventures Of Batman & Robin Alien Storm Clayfighter Columns Dr Robotnik's Mean Bean Machine Earthworm Jim Ecco The Dolphin Eternal Champions FIFA 96 & 97 Judge Dredd Kid Charmeleon Mortal Kombat I,II,III Shinobi Sonic The Hedgehog Street Fighter II Streets Of Rage Toy Story
I don't think the best MD games have aged as well as the best SNES ones. I used to enjoy Ecco The Dolphin and that is still a good game. For multiplayer Gauntlet 4 and Wiz n Liz were both very good at the time but I haven't played them in ages.
Apologies for breaking up the Welsh monopoly with some further suggestions
Road Rash - Comic Violence with some racing bolted on. Comix Zone - Late release IIRC but showed off what the the megadrive could do. Streets of Rage 2 - First one was great this took it up 10 knotches The Immortal - Nice isometric action adventure, goblinbashing tastic Shining in the Darkness - Probably not everybodys favourite RPG on the MD but a quality none the less. Toe Jam and Earl - Just Wierd. Desert Strike - Not played the sequels to any great extent but this was great for its time Dune 2 - Admittedly this was played more on the PC but the games importance to the RTS gerne makes it special. Sonic 3 - Not a major fan of the blue ADHD hedgeog but this was the best installament. Shadow Dancer - Shinobi + a mans best friend = WIN