Honestly the only real problem I see is the horn it's a little out of proportion but thats the only bad thing i see. Now to write about the good things i see I really like how you did the whole "light and shadows" kind of thing I also like the how you did the mane.
And the utility barding was done nicely as well another thing that I also think that you did a great job on the background.
Anyway over all this is an awesome piece with no really bad problems and a lot of good things. So yeah I just really like this Piece