Hi Adam, I like your map. Here's some feedback, perhaps useful:

The magma doesn't look much like magma (more like brown, lacquered wood at first glance), and the grass doesn't look very grassy; their textures aren't isometric, which makes them look out of place, as opposed to the stone floors which look great. The grass texture would look less flat if you made it darker but left a bit of bright texture in the middle, creating a path to the entrance,.

If you are planning to print this map I would also fix some of the edges. The high contrast areas like the text and the isometric grid with 1 pixel wide, hard edge and no anti-aliasing could be especially problematic, even for a good quality printer.

I like how the lowest level reminds me of Diablo, I love old games. Also I wonder how you created your map, would you share a bit about your creative process if you have a spare moment?