Very nice - as you say the grid needs to be slightly heavier in some pages, but don't make it too heavy so as to dominate the map. The maps are quite lovely. I have some observations:

1) the water in the first map is really nice - it's got a real sense of depth and of light. The water in the third map does not - I think because it is deeper? I recommend you try and redo what you did in the first map (presumably blending the layer mask at the edges to a much greater extent) and also add overlay highlight to one half of the water in the third map, so as to show light dappling the surface and break up the regularity and sameness a bit.

2) The blending out of your rubble layer isn't great. Rather than blending it with the smudge or fuzzy-edged tool, you should create crisp edges on a layer lask with the crisp-edged paint tool. Draw around individual rocky fragments on the layer mask, then add some shadows to break it up.