They've changed the theme tune again; it will take me a little while to get used to it, but I like it well enough. They've also changed the background, and it's now a bit more similar to the "classic" episodes that I grew up with where the Doctor's face appears in the middle; however, it was slightly more subtle this time, with only part of his face merged with a star formation.
The inside of the TARDIS has changed again, although I'm not quite sure why. I understand why they changed it for the film (8th Doctor) and the relaunch (9th Doctor) because the old version might have looked a bit cheap; similarly, I gather that the previous remodelling (11th Doctor) was related to filming in HD. Maybe this new version is better for 3D? Apparently the Queen's Speech was broadcast in 3D today, so it seems plausible that the BBC will do that for other programs too. Anyway, the new look is fine. More importantly, I was glad to see the Doctor wearing different clothes for once, so that he could blend in with his surroundings a bit better.
I do my best to avoid spoilers, but I knew that this episode was supposed to introduce the new companion. I also knew that the same actress appeared in Asylum of the Daleks (where her character died). Since this episode was set earlier in history, I assumed that Clara would be an ancestor; they did something similar with Gwen in Torchwood. Anyway, it would make an interesting change to the last few companions to have someone who isn't from the "present day".
This episode brought back a few characters from A Good Man Goes to War (Strax, Vastra, and Jenny), so it was good to see them again. I'm not quite clear on how Strax came back from the dead; I initially assumed that he was another Sontaran from the same clone-batch, but apparently he got resurrected somehow. Have I missed an episode somewhere? The scene with Strax and the memory worm really did make me laugh, and I liked Strax's ongoing suggestions of heavy weaponry. Vastra and Jenny didn't come off quite so well, because they seemed to be too reliant on the Doctor, but I really liked the scene where they were interviewing Clara (the whole business of one word answers).
I mentioned the theme tune above. When the Doctor was claiming to be Sherlock Holmes, I'm pretty sure that the background music was copied from Sherlock; not quite the same, but certainly inspired by it. So, that was a nice touch.
When Clara was telling the children more of her "completely true" stories, that reminded me of one of Rewind's lines from the Transformers: More than Meets the Eye comic: "A totally epic story based on real events that definitely happened."
When Clara went into the TARDIS and asked about the kitchen, she mentioned baking souffles. This implied that she's the same character from Asylum of the Daleks. She didn't recognise the Doctor in that episode, but this episode helpfully introduced the memory worm: a brief touch will wipe out an hour's memory, and holding it for too long could erase decades. Pragmatically, I know that the cast of Doctor Who tends to rotate every few years, so I wouldn't expect this new companion to be around forever. However, this seemed fairly bleak: she'd travel with the Doctor for a few years, then they'd part company and she'd lose her memory of ever meeting him. She'd get on a spaceship, which would crash, and she'd turn into a Dalek, and then she'd die. Based on what happened with Amy Pond, we know that the Doctor wouldn't be able to change that, and based on past experience with River Song we know that Stephen Moffat likes having characters who meet in the wrong order. Still, it's not exactly a happy ending to look forward to.
Later, Clara fell off the cloud. I assumed that she would survive (in order to die later), but I couldn't see how the Doctor was going to save her. How quickly can he move the TARDIS? Then she went crunch on the ground, so apparently not quickly enough. From a first aid perspective, I'm slightly dubious about the idea of an impact that would be severe enough to kill someone without leaving any obvious marks, but I'll let that slide.
At the end of the episode, they mentioned a disembodied intelligence that would be attracted to the London Underground. I assume that this is a reference to The Web of Fear (when the 2nd Doctor fought Yetis); I haven't seen those episodes, but I've heard of them. Dr
I didn't watch the "trailer" after the credits, because I want to be surprised, so please don't tell me anything that you saw there. Anyway, roll on April!