I'm not a music master or even a major composer, but wow, this is top tier stuff. Songs like this are proof that skill/effort/talent does not always equal success and popularity. It's sad, but it doesn't make the song any less incredible. I suspect under different circumstances or with enough exposure, many people would find this track beautiful.
I think the use of syllables to convey emotion and sound are great, it adds a very... ethereal quality to the music that transcends language alone, like a unique type of choir. Truth be told, I generally dislike lyrics or vocals, but I don't mind the ones here and I suspect the "non word" singing is what did it. I would like to hear a little more of it near the end, personally.
Truly, the only complaints I can levy against the track is around 0:59 the voice is a little loud compared to the very quiet and subtle piano. I had my volume a little higher to hear the piano and was a unpleasantly surprised by the volume of the voice, even though it sounds great when I have my volume proper. The second would be the last minute or so is a little too subdued for my liking, though I suspect this is just a "me" thing and not really an objective criticism.