River Tiles has potential to be a really neat little game, but is seriously held back by the lack of clarity in the rules, and would strongly benefit from more structured gameplay.  For example, a "levels" system with predetermined layouts and predetermined sets of tiles, all visible from the start.  The flood starts when all tiles are placed, and the passing condition would be for all of the villages to survive.  A tutorial level would mesh well with this.  Levels could even be grouped into "worlds" that use different tile sets, but the same gameplay, or new tiles could be introduced in each world (ex. something that blocks water as long as only one water tile is touching it, but that water passes through if it's exposed on 2 or more sides).  As it is right now, it feels like an alpha for something bigger.