Hrm... a decent rendition. The 'itsuka' in the beginning sounded a bit more like 'itsuke' though. I'm impressed with the singers being able to keep up with the fast onslaught of syllables in the song, and the harmony was pretty well done. However, it seems that the two singers are reaching at times, especially for the drawn out notes, and that causes them to go off pitch.
As for lyrics, the romaji and the translated lyrics are at:
http://www.animelyrics.com/anime/kannazuki/knmagony.htm
(I do not vouch personally for the correctness of either, but at least the romaji should be accurate)