I love this tileset; the mountains and coastline are beautiful! I've used it for a few games now and it looks great, but I can come up with a few complaints and suggestions.
1) The invisible jungles that were mentioned before, and it happens with forests, too.
2) Some forests look like jungles (the shiny green leaves) and some jungles look like forests (the dull green leaves).
3) The coastline is curved, but all irrigation is square, so irrigation on the shore overlaps the beach and water adn messes up the natural-looking coastline.
4) This is personal taste, but the deep ocean is really dark, almost black, on my monitor. It's hard to tell the ocean from unexplored fog.
Hey, those are just nit-picky details! It's great overall!