First of all... post in another part of the forum

(Halls of critique or the screenshot thread for example)
My suggestions:
-More little things like plants or rocks to make the floor more interesting
-Also, you could place some stuff on the walls
-You have a lot of non logical spots were edges are missing etc., try to use shadow tiles or something like this to make it more plausible
-There's shadow missing on the top most part
-don't use connected tiles in 1x1 square fields- like on the bottom right part. it looks to much like rectangles (and normaly you want to avoid a rectangle like look on outdoor or nature inspired maps)
-get a bit of extra color (plants, little grass patches) into the map, and maybe special effects like sunrays
Hope you can make use out of my suggestions