Nice idea. Some tips for improvement: vary terrain elevation a bit, paint some height and then use the smooth tool with a large radius and small weight/hardness to reduce the jagged polygon edges. Also, if you paint roads etc., make sure to paint with low weight and hardness too, so that you get blurred edges, not the jaggies you currently have.
A last thing: although themed maps might seem cool at first, they can become boring, because balance is more important than cool looks or fun architecture. I'm not saying your map suffers of this problem, it's just a mistake many new mappers make, to focus on cool looks instead of gameplay.
