looks like you got lazy with the drawing work around the top area, its just not the same as quality as the rest.
your lines are a little too soft, harder lines, harder angles with more precise shading work.
design around the eyes is boring, that <.> eyes are so 2009.
the visable brown area is too smooth, i dont want to see a blank background.
Needs more contrast in the metal shading, looks like plastic or clay. less black shades and more pure white highlights. the black should be less common, should only be used to make certain shadows really pop.
clearer definition between the highlights and the shadows.
some of the shapes dont feel natural, however, I dont know how it looks on the sphere, maybe it was intentional, i dunno.
but mostly emphasis on the harder lines and angles, more clarity between light and dark, less black, more white, subtle but strong shadows and bright and vibrant highlights..
i found the shadows in the red highlited areas and highlights in the blue highlighted areas just not strong enough.
and the lines not sharp or crisp enough.