totally unnatural tree color. no composition whatsoever. Very weird perspective (the grass is the exact same size even in the far away plane). No aerial perspective. Very, very poor color variation for such an environment. Mountains are usually covered with forests and grass, therefore they are green not grey; there are only several spots barren cliffs, depending on the mountain's environment. The shadows have the same saturation value as highlights. The trees don't blend in with the background.
That's about all I have to say for now. Overall way below average, but keep practicing by copying existing environments so you get used with the color ranges, how light falls and reflects, the color variation, perspective and so on. Right now you either have very little knowledge of all those or you know of them but don't know how to apply them. Well copying from nature will help, trust me. Never stop working. | 
