So, my thoughts on looking at your piece are that the characters blend too much with the background. Desaturated on desaturated just doesn't really work. Up the color saturation and make the character pop, have him as an accent of the piece.
Besides that, the characters and building standing on the very bottom of the image looks bad, MysteryMeat proposes an easy fix to alleviate the issue.
Also, in regards to "it's not needed", the details are what make something have character. The silhuettes, I think, do not work at all. Use colors, poses and composition to draw the eye to the main character, and have the characters themselves be a backdrop, but let them be "alive".
To illustrate what I mean I'd point to any Ghibli movie. Their backdrops and background crowds are amazingly detailed and animated, and give life and, most of all, realism to an otherwise unbelievable world.