Looks very cool. Just a couple thoughts. The coast lines and lake coasts are a bit too scattered I'd smooth them out just a bit and keep the small islands, they look very good. The climate zones are too abrupt. What about using a softer brush and maybe downsize the flow on it? You could also play around with gradient setting for climate zones and then adjust them manually. Lighter "sand" patches within desert and plain could also work well and give it some realism.