Try to work on body definition and the details. The shirt wrinkles are way too large and not shaded correctly. If the light is coming from the top, then the top part of the wrinkle will be lighter then the shirt color and the bottom section of the wrinkle will be a shadow. Not to mention the wrinkles are put in wierd places that don't match his anatomy, but I'll get to that.
His legs and arms don't have any muscle definition. The only reason that the picture looks like a human, is because it has a head, 2 arms and 2 legs. Try to show the bicept, tricept and elbow instead of such a strait limb. If you dont understand, look at his pants and crotch area. Doesn't seem realistic, eh?
