I think having the back walls in the back corners of the map is a nice idea to reinforce how it should be envisioned but you do not need them everywhere. The transparency just does not work for me sorry.
I also think it would be better with a more solid background, it sort of gives me the feeling now of the place floating in the clouds rather than being underground.
hmmm that could be a nice touch, no walls, just the flooring and bottomless chasms on either side
Overall a very nice job, glad to see how even the mostly clueless artists could take those pieces and turn it into something worth showing.