I think that the rivers look fine. Most folks tend to make rivers all swurvey but at this scale they don't really look all curvey. Making them curvey-cool makes them look like they were hand-drawn but jaggy rivers look kind of digital. So the only real fix is practice. The main thing catching my eye is the shelf - it seems to match the coastline too perfectly. What I would do is take a spatter brush and brush some areas that stick out from the coast here and there and generally make that shelf have more variation in shape so that it doesn't follow the coastline so perfectly. Either that or blur it so that it isn't sharp. You could reduce the height of the bevel itself from like 100% to 30% as well. Looks really good, though, with everything else.