For me it is the lines in the water (can't remember what they're actually called at the moment). The texture/color fading beneath them looks just fine, but I think the actual lines themselves are maybe a little to thick and/or intense. I would try something thinner with just enough opacity to be visible. Also, you might consider doing the rivers with the same texture/color as the lakes and seas. That might make things look a little more consistent on the whole. These are just nitpicks, though. As I said earlier, this looks good for a first (digital?) map. Looking forward to seeing more from you.