Sonic CD comes first is a lot of people's minds. "Sonic Boom!"

Popful Mail is a great, underrated platformer with JRPG-esque coating.

Amazing Spider Man is game you must beat in 24 hours.

Batman Returns, if you get past the driving stages.

Puggsy, Woody, Heart of the Alien, Pitfall, etc. Don't know if they're any good.

But why restrict yourself to platformers? Sega CD well-known for great shooters and RPGs too.