Pretty good for a first try ok, a few comments though:
- About labels : try avoid the PS/GIMP curved text tool that stretch text in a bad way. Prefer using the path tool to build your curved labels. There's a quick tuto by Thamupp in the Tutorial sections if you don't know how to do it.
- About rivers : yes they need to be re-worked. The size seems very big regarding the other geographic elements size and you better check the "how to place rivers" thingie in the tutorial sections aswell since you have some issues with them for now.
- About the brushes : I conciur with Jfrazier about the blurry city icons and the swamp symbols size. Your icons are blurry because you probably scale them up/down .
- About the color : The map seems a bit dark to my tastes.

Anyway, good luck with your mapping projects!