It's not often the Christmas Special ranks this high but when one features solid performances from every single actor, scary monsters and a plot without any noticeable holes, it would be churlish to place it any lower simply because it's intended to be nothing more than a piece of festive fun. At least, that's the usual purpose of Christmas specials, but this one actually advanced the larger plot, reuniting the Doctor and Clara and resolving the lies told at the end of Death in Heaven. Finally, the two series leads communicate honestly. Fans, of course, guessed that Santa would be revealed as part of the dream state caused by the alien creatures. They also guessed that the possibility of Santa being real would also be left open. In fact, fans pretty much foresaw everything that happened in Last Christmas, except for Shona's dance routine (which was totally awesome, by the way). As for Shona's choices of TV viewing being the reason for the dream being an Alien vs Miracle on 34th St mash up - that revelation was sublime.