The style of this tileset is wildly inconsistent. The ground is bright, straight, and anti-aliased; the hair is more "scribbly" and is plain, sharp pixels; the background and harvested bamboo are both quite smooth and blurry; the unharvested bamboo is in a style similar to that of the grass but is extremely bright, and the house is a mish-mash of all those things which is appears to be drawn in two different perspectives at once. Inconsistency in style is never good.
In general, plain primary colors are bad, as are extremely bright and/or saturated colors. There are plenty of exceptions, of course.
So, improvements? Pick one style and one perspective, and stick with it for this tileset (and any other tilesets used in the same level). Find some more subtle colors, and maybe give the ground tiles a more interesting texture. If you want to add more tiles, I suggest more houses and bamboo, some other plant life, and a second set of ground tiles.