I love the rockface and slope areas: the colour choices in particular are spot on. The grass however is a little plain and has some "grid" left in it. I'd suggest adding in another type of grass (probably a lighter shade) so you can make some more interesting patterns. Either that, or add in dirt tiles.
Also, I'd like to see some kind of connection between the trees and the grass. Maybe some roots, or just some more grass growing up by it?
Finally, I think some shadows under the trees in the top-left could give the scene a big visual improvement.