It really depends on the types of games you enjoy, plenty of games came out only in Japan but never got proper translations, mostly being RPGs or similar titles. Also there's Golden Axe III and shmups like Panorama Cotton. The best exclusive games seem to be pretty rare and expensive.
There's also several North American games that never got released anywhere else. I think Frogger was one of them and Pirates! Gold was another. I still want Scooby-Doo Mystery at some point being a good adventure game, though this also had a Brazilian release as well.
Nobody is mentioning the other exclusives from places like Brazil, Australia, and Europe.
Plus taking out all those games mentioned like sports, licensed, simulation, etc removes a lot of good games as well, sure most licensed games aren't great but plenty still are. Even sports games can be fun on the Genesis, it's one of the few consoles where I would even consider playing sports games, along with the NES, SNES, and maybe Gameboy for some titles.