I like it. I like the rough walls in the top and the right part of your map. I would add it to the whole of it. Or add some other type of wall in the smooth walls section, like wooden beams or some other reinforcement.
You can decoratie it, but if its going to be a battle map or a hand out, the players already know what will be in the next room.
It's very nice.
I like this map...The only thing I would change is take the stroke off where the water starts falling and maybe define the mist a little more...but really that is not that necessary.
I am planning an underground city map, but I am stuck on how to go about it.