what babydoll said.

and Crystal caverns, with crystals thats actually
reflects light or anything in its surroundings.

No reason not to go all out on SE's state of the art graphics quality.

a forest like "sanctuary of zi'tah" from FFXI, or atleast the
same type of mystical / erie music to go with it.

Snow / arctical areas, and when i say snow i mean so
much snow you would be up to your knees in it,
insane snowstorms & slippery...yes slippery ice patches on ground.

And dont forget making the sounds of falling snow, wind, ice-crackling
properly to make the game so much more engulfing.

Just adding such a small element such as slippery ice patches
will bring a whole new difficulty to the game.

Or...if you stand too long on an ice-patch you will be frozen solid lol
(hinting some new Raid difficulty elements for you guys on the dev team)

Just Do It !