Fantasy Zone 2 might be the most beautiful 8-bit game ever. It's also really, really fun.
Dragon Crystal is a pretty hard roguelike, but I really like all about it. Give it some tries if you can (it'll take some time to understand it).
I was doing fine with Dragon Crystal on Game Gear (3DS version) till I ran into a big eye or something that insta killed me. I was like what the hell do I do to beat that enemy or do I run away.