Ys III is pretty amazing, even if you've tried the 16-bit versions.

Final Fantasy III is totally playable in japanese and the visuals are very similar to FFIV. I also played through the Famicom version of Final Fantasy II, but I wouldn't recommend it unless you're a hardcore japanese RPG player.

I haven't played through Destiny of an Emperor II (Tenchi wo Kurau II?), but it looks like more of the same, which is a good thing.

Gradius II and Parodius are very impressive and still very playable.