Zelda is, IMO, a pretty unclassifyable genre. It has elements of several different Genres, but never really enough to classify it as a certain genre. It has very light RPG elements, very light Adventure elements, moderate Action elements, and light platformer elements.
Yet, how much does it really have in common with Monkey Island or Myst? How much does it have in common with Final Fantasy or Phantasy Star? How much does it have in common with Mario or Sonic? How much does it have in common with Apocalypse or MGS2?
There\'s several games out there like Zelda which defy classification. I prefer to simply call it "Zelda".