hi, TStrube

I am not an expert at all, so please remember that my opinions are worth up to a certain point and not beyond!

I am assuming that the area depicted in your map is part of a bigger world, and the central mass is some big island/small continent
I appreciate the overall appearance of the land masses and by the way, for somewhat reason, i like so much the look of the smaller islands in the "south"

I have used myself the brushes from Star raven, and i think that your mountains are looking fine: however, i would like to see less... mh.. how can i say. Less clear cut separation between the various areas.
Maybe putting some more isolated tree between the mountains, or placing a couple of hills in a more southern position... perhaps what is disturbing me is the lack of vegetation around the rocky area: a tree or some bushes in the river valley? Probably it's only me, wait for more professional advices!

The river in the central part of the map is giving me some problems: usually, a river starts from a mountain (there is plenty of discussion on rivers on this forum), and flows to the sea following what i assume could be defined a line of lesser resistance. So, i would like to see a little bit of elevation in the central part of the island: i do not think there is the need for a huge big badass cliff, you can go for lower hills!
In while providing a point of origin to the waterway, the reliefs also influence the direction: so adding a few more elements will give a more natural look to your fluvial system.

I hope my humble ideas would be of some help to you.