Ok, thought after running around in it:
-The entity lights look weird without source (see attached sshot), the light just comes like from nowhere. I'd suggest you to use torches/lanterns in the caves, they give nice feeling. (Take a look at anubis or forgotten_caverns for reference. Both maps have torches)
-Use dynamic light in the low area to imitate broken light (See coi for reference)
-Use vertex manipulation/planes for terrain and walls to make it more realistic
-Detail!! Think something cool, because i can't think anything at the moment.
-2nd sshot, this box is really annoying. When you try to jump from the barrel belove to here, you can hit the edge of this box and you fall. That's extremely annoying. Also the other edge is inside a wall.
-3rd sshot, the box is misaligned.