I personally think the tileset couldnt really be improved shade-wise, its obviously an issue of style (He must like a sketchy style?). But one thing that I do see that could be improved is the ammount of repetetiveness in your tiles. The house for example has ALOT of repetetiveness because of the textures you use.. Try to make a pattern in your textures rather than just putting them into the tile without realizing that the tile has to be used multiple times.
