Watched this on my flight back to Japan but I'm only just getting the chance to comment. I loved every moment of it, although it wasn't quite as wonderful as "A Christmas Carol."
The overall story was a bit predictable but that was easily overlooked by the great rapport Matt Smith and Jenna-Louise Coleman, as well as the supporting cast of Neve McIntosh, Catrin Stewart, Dan Starkey, Richard E. Grant, and Ian McKellan (again, it's a shame it was just his voice but I guess he was too busy with
The Hobbit for a live role). Even I hadn't been spoiled that The Great Intelligence was returning, I'm fairly certain I would have figured out it sooner than later, especially with the underground reference. I'm curious to read how new fans react to The Great Intelligence and whether or not they think its too similar to the Nestene Consciousness and the Autouns.
While it was great fun to see Madame Vastra (inspiration for Sherlock Holmes, such cheek, Moffat!

), Jenny and Strax ("I suggest a full-frontal assault with automated laser monkeys, scalpel mines, and acid.") again, I was much more enchanted by the enigmatic Clara. Doesn't help much that Coleman is cute as a button, but the way she moves from scene with such stubborn grace and curiosity that thrills me. She's like a wonderful mix between Zoe, Leela, Romana II, and Amy, if you see you what I mean. Add on top of all of this, how does she keep coming back to life? I love a good mystery!
A few random thoughts:
Upon seeing Clara as a barmaid in this time period, I couldn't help but think of Ellie from Big Finish's
Jago & Litefoot series.
Maybe because I recently watched the entirety of
Game of Thrones and just started the first novel in the
A Song of Ice and Fire, I laughed when someone (I can't remember who now) said "winter is coming."
I can already tell people are going to either love or hate the new opening sequence. The classic theme disappears ever slightly more and the equence is quite bombastic (in some ways, it reminds me of McCoy's). But I don't care, I loved it. Especially the return of The Face! I am curious to see how fans react to that.
We didn't get much of a look of the new TARDIS console room, but I already love it. Great callback to the classic console for so many years. I can't wait to see more of the TARDIS interior.
Lastly, I love the twist from the usual "Bigger in the inside" to "It's smaller on the outside!"
I gave the episode a "very good" but I might upgrade it upon rewatching the episode.