Hmm, I don't like the outlining on the trees and stumps. You might have planned to take them out, but just making sure. The grey you used for shading the clouds is far too dark, and would probably benefit by adding a little color (perhaps blue or pink?) to the flat grey.

Your palette seems to have a bit of trouble. The colors you use in the grass don't show the shadow and grass as much as they do a ring green on a yellow surface, due to low contrast and no texture (an artifact of the low contrast). I made an edit to show you some decisions I would have made concerning the palette, such as decreased saturation and some more contrast:

Edited by Monkey 'o Doom - 27 April 2007 at 6:41pm

If it's the barren dirt and grass, show the dirt as a brown area with cracks and holes, then make an edge of the grass under the tree that shows the transition. Generally it's not so gradual as to warrant dithering to blend colors, and you could free up a few by using a sharper transition between dirt and grass. You could look at a few oldschool RPGs to get ideas of how to pixel the border between dirt and grass.

I think the dirt needs a little bit more shading. If you havent passed the 16 colour limit maybe you can add a shade to it.