This is good to be able to complete the artwork but I think you should have blended it instead of layered it. because this is obvious that you've painted it, when most others look somewhat more natural. Don't get me wrong though, the freehand is great!
There is some really chilling artwork on this thing. Great work! All i can say is try to make your highlights more even and smooth and you will have a truely awesome model in your hands. Keep up the good work!