I think the games people usually recommend are great, but it sounds like you've played a lot of the usual stuff, so:

NES: Fire 'n Ice (puzzle game), Conquest Of The Crystal Palace (hard platformer with sword), The Adventures of Lolo 3 (action puzzle; they're all good but I think 3 is the best intro), Super Mario Bros Flow (ROM hack, joyous)

SNES: Lufia II (whole RPG with great combat mechanics), EVO The Search For Eden (RPG platformer about evolution, weird as shit, grindy, kind of a trip), Demon's Crest (hard as shit platformer with rpg/metroid mechanics), King Arthur's World (RTS), Ultima 6 (open world RPG, completely unlike the SNES RPG canon)