To me, an RPG is where you do about as much talking as you do fighting, and fighting is turn-based and you level up to get better. You might say the Zelda games are RPGs because you always get more and more health, or not because you fight on the overworld. Does Luigi's Mansion qualify as an RPG? I barely think so, but I've read somewhere about it being almost one. You don't level up, but you do talk quite a bit, and you have to find special items in order to progress.