I like it. Reminds me a bit of the cave tiles from Frogatto, or--wait for it--Cave Story. Good job with the direction you've chosen.
Only small problem I have is that the background rocks farthest from us (?) don't seem to fit in, almost like they're from a different cave entirely. Mainly because of the rock structure, but also because of their colors. And they might stand out too much, as the colors they used are almost brighter than the rocks one layer closer to the foreground. This could make things confusing and incoherent, bad, of course, when you're talking in-game levels, or even just a mockup. They might need reworking.
EDIT: Highlights on the foreground rocks don't suggest a clear, unified lightsource. They're pretty much all over the place.