This really reminds me of
Steerpike's Cadaverous Earth, over at the Campaign Builder's Guild, from what I can gather from this map. Very cool in that "dark" kind of way.
As for your rivers, and where they meet the coasts, it looks to me like the issue is that you can see a "river" come up to the edge and stop, as it overlaps a coast line. It might help to erase the coast line right at the rivers, and make sure the color on those rivers don't go out into the ocean awkwardly.
Consider the possibility of having the coastline brush also border your rivers. Doing that would incorporate the rivers into the look of the rest of the map, if it doesn't end up looking terrible. I'd say play with that, and if it's bad, just don't save the changes.