your painting is too flat. you need to add more details, especially on the eyes and flank. try blending the lineart into your painting; it'll make it look softer and more realistic.
Add darker tones in places where the skin is overlapping: like under the snout and around the knee joints. dont soften the shading on the hoofs; itll help it look more like metal.
keep practicing and im sure youll get better =)