There are a few things that I can't quite put my finger on, but here are a few I noticed:
1: Your tiles overlap all funny. Bricks shouldn't go over grass or anything, really, other than dirt and rock. Change the order of tiles in the "Advanced - Modify Tileset"; a tile that is to the right of another tile on the list will go above the other tile.
2: Not only are cliffs not preferable, but the ones you used are horrid. Why use a lordaeron dirt cliff in the middle of a dark ashenvale forest?! Just don't use cliffs at all, they only cause problems...
3: The textures you use don't blend so well. Dark models shouldn't be put on light tiles.
4: You should variate your tiles more, or at least make it so it isn't huge blotches of one tile, then a huge blotch of another with roads going through them.
