Desaturation shows you exactly what tonal values you're using. A good range of values will go a long way in creating depth in an image.
A few ways you could've achieved this, would've been to, say, make the armour plates of much higher contrast, or to use the sword as the only light source, so the directional lighting would've made it a lot more strong, contrasting and overall appealing. If you want, I can make a quick sketch based on your art, to show you what I mean.