Well, sort of. I was looking at it more from an artistic perspective or, well, you'll see what I mean. You know the landscape painting rule that says "cool colors recede and don't put warm colors in the background because they'll jump forward off the page and kill the viewer" ... or something like that, haha! I'm very tired and have forgotten how to more accurately and succinctly explain my point (for anyone who is curious enough to read on, I apologize), but anyway... contrasting values can have a similar effect.
In this case, your solid black lines around the cliffs work better in the areas where there is a distinct change in value on either side (the natural edges of light and shadow) and also in the shadows where the value is the same on both sides but also darker so there's less contrast between the line and the stuff around it. It doesn't work so well in the areas where both sides of the line are lighter, like at the base of the cliff; it throws off the local depth perception, making it difficult for the eye to interpret. If you were to use some kind of technique to soften the lines in the "light|light" areas--perhaps using a thinner line to keep it consistent with other parts of the map, or using a broken line, or other options, it might help things read better while keeping your mixed line art / realistic style intact... which is quite nice
and I'm going to sleep now.