Hmph.
My critic might be extremely biased, as I study in an art academy, draw live models three days a week and get bitched on at the slightest mistake. As Jeebs said, you screwed up the proportions, not to mention the body's structure and depth. The guy has an extremely big head and a down-syndrome body. I advise you to google up anatomy or study anatomy books.
I like the coloring, although it lacks contrast and real shade/lighting.
One of the best things that have showed up so far, so don't stop drawing. Practice. Perseverance!