There was so much to like. The snowmen were beautifully creepy, brought to life with some perfect special effects. Simeon was a brilliant villain, though I would have liked to have seen more of him. The reference to the Great Intelligence and the London Underground map was very unexpected. I thought it was a brave move, though I can see how it'd go over the heads of some people, since it hasn't appeared since the 60s in The Web of Fear. Vastra, Jenny and Strax were wonderful. I hope Vastra's role as somewhat of an equal to the Doctor is shown again in future episodes, as I loved the scene in the TARDIS with her and the Doctor. Speaking of the TARDIS, the new interior's pretty good. I'm not massively fond of it at the moment, though it looks amazing while in-flight.
Clara and the Doctor were both exceptional. I admired her persistence, though she seemed a little too persistent, don't you think? She adapted suspiciously quickly to the Doctor's life. I wonder if it'll tie in to the mystery of who she is. I have to say, I saw the modern day Clara scene coming as soon as Victorian Clara died, though I really don't know about her true origins (she was born on the 23rd of November, hmm...). I want to see the first episode of the April run so badly now. How will the Doctor approach modern Clara? Will she know him?
It was all so magical. The staircase to the clouds was so awesome, as was the Mary Poppins reference. I am definitely watching this again tomorrow on BBC Three; it was near-perfect. The pacing was great, too; it really felt like an hour of Who, yet it never dragged.
The titles are very cool. I love how funky and cheesy they are. I would have preferred a greater influence from the Classic series in the new theme tune, though I guess I'll make do with the warbling-thing (I really don't know what to call it - it's the noise heard right after Matt Smith's name appears. :P).
The resolution was a bit iffy, but I felt it worked. I think it makes sense. It was evident that the episode was more about Clara than about the Great Intelligence and its snowmen.