So, slight update. I figured out what was bothering me about the walls. I was trying to imply the rock-forms with shapes like this:

And that's not really how it would look. If anything, it looks like some cracks in the wall. So I threw together a rudimentary model for ref (
this) and managed to improve the wall somewhat.

--->

I like that it looks more realistic (I guess), but it is also crazy repetitive.

I could try to find a middle ground, but the new one seems to have less "charm" so I'm not sure it's worth keeping.
also might be a pain to redo the floor in the same style...Are you going to be adding an actual lighting system in the 3D program?
I dunno actually! I tend to like the look of a skylight with textured shading, but I'll at least throw on a depth-of-field effect so it's not so overwhelming. Lighting is one of those things I make up as I go with projects like these.

What about details, it's really a matter of choice and style. Think Chaos Engine, for example. Their floor tiles were basically just a solid-color fill with some simple corner details. You shouldn't make tiles too complicated, however, especially when they are going to be repeated frequently and on large areas. In the above case, I think that you haven't crossed the barrier yet--the set looks good!
Thanks! I've never heard of Chaos Engine before, but a quick image search fixed that. Glad you think my stuff is working as-is.
I know you said you're pretty set on your color palette, but take a quick look at this. It's just a quick edit of color levels, but I think it is more representational of basaltic rock.
picture
IMO, the level of detail is fine; the floor tiles complement the walls. I would say that the shading around the edges of the floor tiles seems to round out the appearance of the tunnel. You may want to edit that a bit if that is not the desired effect.
The rock isn't actually basalt, it's just a fantasy-land rock that's the same style. Apparently the correct term is "columnar," which sounds awkward out loud. But hooray expanding vocabulary!

I'm not too concerned with the roundness, it makes things a little more organic anyway.
Haha but dangit, everyone seems to think it was pretty good already, so I'm definitely leaning toward the older version of the wall...