I don't have a super expansive Genesis collection, but I can give a few good/descent hidden gem suggestions for the system:
Zoop- If you like puzzle games, this one is pretty unique and fun in 10 minute sessions. It's also on basically any console that was relevant back in 1995.
Wiz 'N Liz- Developed by the same group who made Lemmings, this is one of the weirdest games I've ever played.
Ms. Pac-Man- Great port of the arcade version.
6-Pak- A fairly cheap cartridge containing six Genesis games like Sonic 1, Streets of Rage, and Revenge of Shinobi.
Frogger- Like with Ms. Pac-Man, this is a good port of an older arcade game. Also the last Genesis game released in North America.