Wow, this is an amazing mine/cavern system Jax! I agree with MMM, the impression of vastness of the place is awesome and it has a wonderful organic feel to it. The scale and placement of these settlements add a lot to the overall vibe. I really enjoy your colour choice here (as always ) and the scene you envision together with the map is totally immersive. Brilliant and inspirational work! I'm sure your players will be happy.
Btw. did you use the gimp script for the contour lines? It looks quite familiar