I absolutely love this piece!
The first thing I noticed about it is that it has movement, which instantly attracts your attention. The birds and the streams of wind in the sky really add interest.
Secondly, The contrast between your choice of light and dark is astounding.
You even softened this line by adding a misty haze around the mountains, which gives them presence. I like how you blended the clouds, too; it's easy to envision them moving.
The cool thing is that you've still managed to make your character the main focus in this piece.
Overall, very balanced and well done!
Warn: I do not speak English (Russia). Picture simply magnificent (like the book). But would like to find out what the icon on the far right edge of the picture (just above the middle). It looks like a piece of a program.