"Last Christmas" is the 2014 Christmas special of Doctor Who, starring Peter Capaldi as The Twelfth Doctor, Jenna Coleman as Clara Oswald, Nick Frost as Santa Claus and featuring Samuel Anderson as the deceased Danny Pink.
I have been in the habit of reviewing every episode of Doctor Who for quite some time, a habit that I grew out of midway through the current, eighth season. There are single episodes of Doctor Who that have, in their quality and impact on popular culture, are as important to review as a feature length movie. And there are episodes of Doctor Who that are weak retreads of already presented concepts and characters, and that are forgotten as soon as they are released. There is a fairly widespread argument that the show is not as exciting as it was a decade ago (!) when the revival begin. I don't actually fault the show itself on that: it is just that the cultural contribution that Doctor Who made to the resurgence of "fandom" has run its course.
With that being said:
"Last Christmas" is a story written by Stephen Moffat, and it reiterates many of this themes and concepts. It just happens to do it very well. I can imagine that if it was released in 2006 or 2007, it would be hailed as a classic. Its primary antagonists are "Dream Crabs", parasites that entrance people into immersive dreams while the Crabs feed. In a reversal of the weakness of Moffat's most famous creation, the Weeping Angels, the Crabs can sense when people are thinking about them, so the first defense is to not think about them. However, since the Dream Crabs can create such realistic dreams, how the person who has "woken up" know whether they really have at all? The story manages to release a number of surprises while the different layers of dreaming are peeled off, and I had the fun experience of actually being surprised about what was happening in the story, and confused about what was coming next.
Even though the story borrows from movies such as Alien and Inception (a debt it admits to), it still manages to feel new and innovative. How much I liked this episode is, to me, a sign that the series still has a lot of potential to be innovative, despite what some of its detractors may say.