Season 7's Christmas special was the official introduction of the new companion Clara as played by Jenna Coleman. Of course she had appeared previously in the show but this is where her story really begins. And her interaction here with Matt Smith's 11th Doctor, just like the previous verbal sparring in Asylum of the Daleks is the high point of the episode.
The core of this particular story is the Doctor finding himself again. He's essentially moping after what happened with the Pond's (okay I'm not being very sympathetic... but it's true) and he's largely cut himself off from interaction with the world. Not completely though, which is the first hint that this isn't really what he wants.
This is also the point in season 7 where the emphasis on the series history really starts to become noticeable. Watching it again I'm reminded how much I like the latest version of the title sequence which incorporates so many elements from the past. But that's just the start. Here we get the Great Intelligence and references to the London Underground (The Web of Fear). We get a new TARDIS interior, my favorite from the new series, which while not the old style console again has more elements in common with that than we've previously seen.
As with much of Doctor Who during Steven Moffat's tenure as show runner this story is more about atmosphere and the feelings it evokes than about logic. Those who prefer a more science fiction approach probably won't like it. Clara's death gives the story its heart. Yes it's another power of love storyline of the type that some hate.
And yes you can pick at the details pretty easily here. It's a story that relies on a fair amount of coincidence, all be it wrapped up in the notion of the universe as an entity. The larger story arc of the season will eventually address some of those coincidences, but you don't know it while watching this.
Moffat was pretty clear when he took over that his vision of Doctor Who is heavily influenced by the feel of fairytales. And it's that, more than science fiction which gives us these sorts of stories. I'm very happy with that, others not so much and I think that's one of the big sources for the criticism that his run receives.
So here we have lots (and lots) of faux-Victoriana. Basically it's Victorian England as we see it in our heads rather than as it may actually be. We have blatantly incongruous elements like Madame Vastra and Clara herself and yet the resulting mixture, for me, is highly satisfying.
The acting across the board is great here. But Richard E. Grant as Doctor Simeon deserves special attention for being able to so effortlessly move from arrogantly supercilious while in control and then seeming old, scared and cowed when the Doctor challenges his core belief in what is happening.
I don't think this is an episode that's going to wear well on multiple repeat viewings however. The story itself is really quite shallow. And while it sets up a lot of things, there's not much depth here. It's fun and Christmassy and has me looking forward to re-watching the rest of the season but I'm not in a rush to watch this particular episode for a third time.