EO is plenty chalenging, thanks to its free-roam gameplay. I went down that hole in my first test play, not knowing what was down there... and got my butt kicked in 6 seconds flat. I could kill spiders, but not ghosties. NH is also planning on adding some tough bosses, as before, so I think difficulty is pretty ensured.
This brings up an interesting idea for me. What about special battle-only terrains? For example: Lava that kills you in battle, but does nothing outside of battle, icy floors that make you slide - in battle only. Stuff like that.