Well, glancing at it the first thing one notices is the horizontal lines the highlights in the grass create. Try breaking up those ridges as they make the tiles look... well, tiled. You want it to have the illusion of being a whole piece. Also, consider making the grass edge tiles include the dirt with some light shadowing to help ground them there. This will keep it from looking like the grass is hovering above the dirk like clouds. Lastly, try having a few blades of grass pointing downwards. This will make the scene look more like its being seen from an angle up above rather than from the side. No time for a edit now, and I think you'd rather have one from a veteran anyways.
