I was already astonished by the artwork of reference and I took five good minutes to "get back to the real world" and prepare my mindset for this piece which, in my opinion, is equally beautiful or at least able to compete with it.
Mastering sounds professional and it reminded me of Assassin's Creed II at some points, might have been the vocals used or the relatively acoustic sound. Celtic music always manages to sound awespiring to me and this piece makes absolutely no exception.
I would have made the melodies a little more intense and present in the mix while possibly introducing a theme variation by the time the main theme is repeated for about the third or fourth time. You've played around repetition by varying the instrumentation and playing with the beautifully executed atmosphere. Again, it's a minor discrepancy that doesn't really detract from the experience at all, mere nitpicking if you wish, and it doesn't drift away from the fact that it's a near-masterpiece able to compete with film score and what the industry offers.
Superb job
//FD