One of the best imagges i see so far. Just one thing - color.
When black is used on materials, it should never be absolutely black in the resulting image. Such a color then represents a "hole" in the image for the observer. The human eye always tries to see some reflections and shadows on everything, etc. Some gradient - this determines the surface distance in space (among other things).
There should never be an RGB of 0,0,0, or 255,255,255 in the resulting image on a larger area. But this also applies to other colors.