Seganauts... recommend me a Virtual Console games for the Genesis/MD.
Ristar
The game Sonic Team made after Sonic & Knuckles. The opressed people of the Valdi system pray to the legendary hero, but instead their cries for help fall on the ears of the Hero's son, Ristar. Ristar can grab objects with his hands and throw himself around arenas. The game starts out simple enough but starts to get unruly difficult near the end, if you ask me.
Toejam & Earl
Basically a Roguelike without all the RPG stuff getting in the way. Two space aliens roam an isometric earth picking up presents (with randomized contents) in an effort to find and assemble their spaceship so they can get back to the planet Funkotron. Very low key, kind of a slow burn, but way fun. Has split screen co-op.
Beyond Oasis
Take the Legend of Zelda but mix it with the influence of Anime, Aladdin and other Eastern cultures. A boy finds a magic gauntlet that can summon elemental guardians and must harness their power to protect the land from a growing evil.
Shinobi III: Return of the Ninja Master
Everybody always cites Revenge of Shinobi, but for me, this is the best Shinobi game, just for the amazing controls. With a three button setup, Joe Mushashi has a hell of a lot of moves from wall kicks to double jumps, sword strikes and ninja stars. Pretty short, though - I think you can finish the game in under an hour if you're good enough (but, of course, as with a lot of games that star Ninjas, Shinobi 3 is pretty difficult - though not as difficult as Ninja Gaiden).
Vector Man
A late-era gem, Vector Man was the closest thing Sega had to an answer to Donkey Kong Country. Vector Man really pushes the Genesis' strengths in being able to render a bunch of sprites on screen at the same time - all of the characters are "orbots" - robots made up of multiple spheres that move independently, and the game uses this to its advantage for some pretty impressive visual effects. A pretty cool shooter, too, though it devolves in to minigames a little too often (if you can pass the weird train minigame it's smooth sailing for the rest of the game).
Pulseman
Before Pokemon, Gamefreak made Pulseman, a side scrolling action game about a superhero who can transform in to a bolt of electricity and travel through wires. To be honest, I've never gotten very far in this because it's kind of difficult, but I hear everybody else rave about it all the time. This VC release is also notable because it was a game that only ever got released in Japan, but ended up getting released in English-speaking territories exclusively for VC.