Beautiful! I really love the coloring, particularly all the soft blues mixed with creamy pastel earth tones for the mountains and ground beneath the horses' hooves. Out of all of the painting, Harry, Snape, and their steed (as well as Nagini to a lesser extent) are all the main focus with their vibrantly brilliant colors standing out from the background. I really love the red horse's white socks. The action and perspective really draws me into the scene.
The small details like the beautifully painted pile of rocks and flowers, the riders silhouetted in the background, the intricate pattern of Nagini's scales and the horses' hooves. Wonderful work!