This is looking great. You seem to have an excellent eye and a good feeling for form and shape.
And you are already diggign into the anatomy so theres not much to say about that either. What I do feel is that you sometimes leaves your pieces abit too rough for example the mech it's so rough that I have trouble reading the parts of the image even when youre rough on shading and blending clearly definign the form is very important you need stable edges. But I love the last pic