Looks like a photoshop of in game screenshots, you just shifted arm positions and applied filters.
But it looks like you shaded the spartans for yourself to some degree, so I'll give you a few pointers on that. The burn and dodge tool are not the only weapons when coloring. So after you lay down your flats, I would recommend taking a hard round brush and using the HSB slider to slightly change the color (Darker or lighter, depends how you want to flow) and gradually blend.
Optional: Your lines do not have to be black when you set up your stuff, If you want to roll with the whole blending thing you can have them the same color as the armor but a bit darker.