add a little bit more light to the darker areas.
plus, take this into consideration, make EVERY color stand out, weather blended, shaded, or whatever you do.
I really like the front part, especially the piece you picked for the brows. Is it possible to use that same shading on the strips below the visor? They look flat compared to the rest of the front.
I'll wait for the added background before commenting on the back much.
The simpler c/p is nice, can pass as hand drawn probably, since every part has significance as opposed to detail for the sake of detail.