Very nice! Something you might like to try is using a large surface texture scan to give more visual interest to areas that don't have a lot of color detail or ink work. The idea is to use a large reference in a subtle manner, allowing it's natural randomness to show through. For example, In the sea area, maybe you could find or shoot a high-res photo of light reflections cast onto a pool or river bottom and overlay it for an interesting yet unobtrusive effect. Play around with the size of the reference and it's layer properties until it feels right. Make sure to keep the layer opacity fairly low though so that it doesn't become too distracting.

A neat example of this can be seen in older movies where naval battles needed to be shot using miniature boats. At a certain ratio, miniature waves begin to look much like large ocean swells when set against tiny boats. I can't recall the exact size ratio, but there's a sweet spot where the relationship just clicks. This same effect works when creating surface textures for mapping or cgi. Large or small, you can trick the eye into seeing a pattern as natural and real if it's got that randomness and variability inherent in textures pulled from direct observation. This trick also works in the same manner with dirt, grass, you name it. Don't overdo it though, less is more.