Very cool! I agree about the hat and the ribbon. You have hinted that the robe has a satin quality to it with those highlights on his shoulder. I wonder if the hat needs a bit of this treatment, since it looks like it's the same fabric? I think the ribbon could use a bit of shading and the text could use a bit of attention as well. The text looks a little sloppy, especially since it's right next to your very well executed signature. I kind of want to see the left edge of the ribbon come down a tad as well.
Love your color palette. Great job.