I can see that a plenty of work went into the metal, however the rest of the soldier (the face is okay) looks a bit under the standard. The arm and the leg look pretty flat, bevel shaded (bevels are the little highlighted and darkened edges, say around his leg, that give it a more 3D feel). Unfortunately, the bevels make stuff look flat, which is good when you want to achieve flatness, but this is not such a time.
My suggestion is to create a small palette by the side with 3-5 colours on it, so that you can easily repick colours from it, if you dont have one already. I usually have a layer with just palettes, something that I can quickly turn off when I need to save a version and something that I can move closer to the area where I draw. Then just paint around, and see what looks good. Remember that you must decide from where all the light comes. Johasu remarked that the armour has a slight blue tone, which may be because it is surrounded by open blue sky. It would not work if this soldier was in a room lit with red alert lights.
The belly, armour, and head, are all pushed forward very much. This amount of weight would make him fall forward unless someone holds him or he has a heavy backpack. You can make a copy of this image and try to draw him without armour just to practice correctly positioning him. Try to imagine where his center of weight is now, and consider that we rest most of our weight on our heels, and we use the rest of the foot to make balance.
Also, it's hard to imagine that the legs are so directly behind each other that you can only see one of them. This is how a soldier could stand when lined up, but not when on guard, on patrol, and so on.
I'm sorry that this is not about the metal, but the metal armour turned out to be one of the best sides of this sprite and you need improvements elsewhere. To improve this sprite further, you'll have to create a more natural posture, or add a heavy backpack if you are lazy or rushed, and you will need to improve shading on the pants and sleeves (and other clothing that comes) up as well.