Agreed - nice coloring, and a nice style in general. I see nothing wrong, in general. The rivers seem to end in closed lines, if you know what I mean? it's nothing major really, but something I noticed. The buildings of the little city icons seem to be "behind" the rivers by a few pixels here and there; again, a tiny issue. I think you have a winner with this map.

Btw: Love the "sunken lands" - awesome touch.