I've always thought it would be interesting to make an RPG all out dungeon crawler based entirely in a forest. With time passing, and needing to do certain things in order to survive. A giant dungeon crawler could really be interesting if you tried to add that element. Also, when it comes to things like that, it's always fun to add some small redundant thing the player has to do, makes them stay on their toes rather than just running around killing monsters, eventually owning everything in existence. I.E. Etrian Odyssey, have you ever played that game for DS?