Tweak the light some especially the shadows they are to sharp and make the model look fake, I would turn down the yellow color of the light down somewhat as well ( unless there is a sun chasing him )

I also believe that if there is no sun ( direct light source) or planet ( indirect lightsource) in view then the viewer subconsiously recognizes the light you used as fake and there for make the image look unrealistic.

Looks ike a great start though