I absolutely love this piece. I really do - it's gorgeous and the colors and tones all fit perfectly together. First of all, the lighting on the horse is brilliant and the shadow and the horse all together make it really fit into the piece.
However, I feel like a horse walking in a field is quite overused, as many manipulations I've seen have a horse simply walking in a field of grass or something along the lines of that. But, that being said, I feel like the light source and the fact that it seems to be coming from lower to the ground and the darkness all around it like it's night but something mystical is happening is quite original, as well as adding to the "unknown" factor, which I like.
The mane and tail are gorgeous - they look like more than one tone has been used and the highlights match the light source perfectly, overall creating a feeling like the horse is actually there and the light is hitting strands of the mane, not just one huge chunk, which some artists tend to do but you definitely nailed it. Same situation with the tail; all of the painted hair is gorgeous.
I also really like the markings that you put on the horse, as it adds to the overall picture. It adds something extra that could possibly just clutter up the manipulation but it just makes it even better. A tiny thing with the markings, just because I'm being nitpicky, but they seem to be a little bit "floaty" above the horse's coat - maybe put the later on overlay?
Overall, the entire manipulation is absolutely gorgeous - it's one of the best I've seen on deviantart, a very very well done. c:
Thank you so, so much! Really some amazing feedback! And I totally agree with you on the marking thingie: first of all I blended it more into the horses' coat, but I wanted them to pop out more, so I deleted it. Altough if I look at it now, they might be a little bit to bright indeed.
But again, thank you!