Firstly; It looks superb, tho there are a few things I believe you should consider:
1) The "depth" (, shading between layers,) of the "different pieces" of the head lacks the kind of depth you used in for example the shoulders; this also goes for the chest area. This also goes in general for the would set, the gray segments uses a larger span of light and dark sub-colors while the red and yellow in the eye is very sharp. This could be due to the texture resolution, if so, I hope you take that into account.
2) The orange color would most probably look better if you made it look like pain that has been added on top of the metal, this could easily be featured if you made it worn down much differently from the greyish metal it lies on top of (you could make it look as if flakes has been worn off).
3) The general shading of the different textures is very different, using different techniques and not using a generic method is sometimes fine, but when as now for example the back portion of the head and the back of the tori has such a great difference in sharpness it really stands out as "blurry" on the back of the head.