God Rest Ye Merry, Gentlemen (traditional) listen / lyrics
This is one that has always fascinated me. In childhood it stuck out because it was so sombre. A lot of traditional Christmas music is serious, I know, but this is one of the few that I find downright depressing in its tone. Which is funny, because the tone often doesn't suit the lyrics: How can one feel these "tidings of comfort and joy" when they are wished upon us so mournfully?
It's also a terribly English song (see also: The Holly and the Ivy), which, again refers us back to the above comment. The rhythm in it is what makes the song stand out. A long, long time ago we used to actually have a carol-sing assembly in school, and this was one of my favourites to sing for this reason: the great big breath you take at the beginning to keep the proper flow between the lines.