It's looking great and that sky is fantastic. As for lighting and shading:
- I think he needs a bit more shadow just under his right knee to bring out the form and show the direction of the light.
- His right ankle needs something to show where it bends. If lighting means it is brightly lit like that then maybe a bracelet will help define its form.
- You have a high shine off his right thigh but his back or right shoulder and right hand is actually closer to the sun and should have a similar sheen.
- The left part of his back along his ribcage might need a bit more shadow since it rolls away from the sun.
- I do think for your message to be a little more powerful there should be some residual effects of his flatulence.