This is looking very good, Newton. I should have been clearer, earlier; your presentation of your idea against a solid background, along with less jpg compression perhaps, made even the earlier version show up as more three-dimensional.
After re-reading bits of
2001, I think I understand that, in order to remain true to your original concept, shading (or should I say "lighting") of the monoliths has to be kept to the minimum necessary to suggest solidity:
... Even in the brilliant earthlight, it was hard to see the object clearly; his first impression was of a flat rectangle that might have been cut out of carbon paper; it seemed to have no thickness at all. ... though he was looking at a solid body, it reflected so little light that he could see it only in silhouette.
... beyond the geometrically perfect shape of the thing, there was little to see. Nowhere were there any marks, or any abatement of its ultimate, ebon blackness. It was the very crystallization of night ... .
(Arthur C. Clarke,
2001 A Space Odyssey)
I'm not familiar with the 3D software you're using; however, would it be possible and effective to use, in addition to variations of shade (in pure tones of grey), subtle variations of hue, with lighting effects giving a warmer or colder effect?
Kumulko! has suggested some interesting possibilities for future versions. I'll add one which could be a variation on the luminous outline. When David Bowman finally "lands" on the "surface" of the large monolith, he finds it's hollow and "full of stars." Possibly a faint luminous and/or starry surround or background for the figure when she appears on mouseover -- as if the vertical monolith then is filled with stars?
In any event, I think it's turning out nicely, and look forward to seeing the finished skin.