You did a great job achieving a sense of depth, your color choices were solid for the subject, and I especially like the definition and sculpting of the features- particularly the area around the eyes. The only improvements I could suggest would be making the bolts in the neck more similar in size/shape, and being a little more detailed with the deformation of the forehead- that part looks partially complete, and while it's not aesthetically unpleasant as-is, a bit more definition regarding how/why the forehead is shaped this way would add to the story. Overall, very well done!