Yea, the banding is hurting this piece a bit. It would look really great if you threw 1 or 2 more shades in there to make it "pop" more and give it a more noticeable light source.
You need to work more with that middle gray between the black and white of the skull, it makes banding that hurt the piece. You should use it to shape the skull more, so that it would give more volume. I'd love to see some AA too.
An old, dusty, floating skull.
Totally normal.
And yeah, now that they point it out, some more mid tone would be nice to give volume, although I think you could do it without adding colors if you wanted.