Yes, the ending song is amazing. I ordered it from cdjapan and am waiting for it to arrive. At work, I listen to it on YouTube, although it is probably posted there illegaly. At least I have already paid for mine!
The ending song is really based on real Shinto prayers, according to
this article I read. It certainly feels that way when I listen to it, like it is a real spiritual song.
I feel that something is missing in the episodes where the ending song is not there. Between the opening and ending songs, we get both sides of Nagi and the whole series. It has a "crazy" side and a "shrine maiden" side, and it is not really complete without both of them. (Although it goes a bit randomly from one to the other and back, at least in this first season.) Between them, the songs bring back the atmosphere of the whole show. That is how I feel.