Funny you should mention those. I was just checking through my NES ROM collection, and ran across
Doki Doki Panic, which was a Famicon Disk System release. Except for the 4 playable characters, it looks, sounds and plays exactly like
Super Mario 2 USA. The real
SMB 2, later released here as
The Lost Levels in an SNES compilation, looks and plays like
SMB 1, but is much harder. That too is an FDS game (which probably explains why it took so long to see it available as an image for emulators).
I also ran across
Akumajou Special - Boku Dracula Kun, aka
Kid Dracula, which was never brought here as a NES game. If you're on an 8-bit Castlevania kick, you may want to play it as a change of pace, or for completeness. It may look cutesy, but it's a fairly hard game.