Something that bugs me is the weird knock/click noise at the very beginning of the song as well as one or two other spots.
Otherwise the singing is nearly perfect (minor things is the "s" sound doesn't sound great with all of the vowels and soft consonants, as well as not pronouncing some of the consonants at all).
Something that I would love to hear in this would be instruments! the voices will still be the main part of the song, you just need something to make it more epic. An example of what I'm talking about is The Hymn of the Faith for final fantasy 10 (there are several versions of it). the voices make the song but the instruments add more to the song, giving it the strength and more of the mood to the song.