As a puzzle, "arrange 9 tiles in a grid" hits some limits pretty quickly. But, the design is amazing: the use of depth to get ridges and waterfalls and hills, the directional flow of rivers to a lake, the bridges that help interlock the rivers with the roads...
Even after saying "sure, nine tiles, I get it," I kept looking back and wanting to know how the next set fit together. I can see this as the basis for something much larger, if you wanted it to be. (4x4 grids! People and boats! A plot!)