Steven Moffatt's excellent run of Christmas Specials ends on a rather flat note.
Don't get me wrong. The atmosphere, visuals, special effects, direction and production are all absolutely on-point. Jenna Coleman and Matt Smith are absolutely brilliant, and there are many moments that ascend to levels of greatness. Unfortunately, Tasha Lem ruins the whole episode. I really didn't understand the decision to introduce a completely new character for one episode only. There are countless other characters who have the same kind of connection to The Doctor who could have been used instead. And, personally, I find her annoying.
If you can look past this, the episode is throughly enjoyable. Well, apart from when you'll be crying your eyes out.