I think you should work mostly on how you're shading this. While it's not pillow shading, you're not shading him with any form as of now. None that I can see anyway, so study up. I'm pretty sure there would me a shadow cast on his face considering his fedora, and what's going on with his left (our right) arm? It should be mostly behind his chest, not molded to it. As Mathias mentioned, what's up with the pants? I would feel like a penguin trying to walk in those. That's just the first few things that caught my eye, so if you want, I could do a quick edit to show you how I would shade this guy.
Do what Mathias said to keep working on him, so that we can critique it more appropriately, and, if you used one, post your reference.