There shall be spoilers ahead, so turn back now if ye'd like to be surprised.
I should start keeping a notebook of my thoughts while I watch things because I remember having lots of things that I thought were interesting or good or awkward or whatever during this year's Christmas special, but I'm not certain that I remember any of the good ones.
Ah, well. Such is life.
I suppose I must first say that the lack of Rory in this episode is disappointing. I was honestly hoping that the three of them would play the roles of the three ghosts. The Doctor would be the past, but only because I knew he had a line saying he was from the preview, Amy would be the present because she's so vibrant and in the now and all that character stuff, and Rory would be forced into the role of the future and he would be delightfully awkward about the whole thing until he got really serious and we would get to see some of the 2000 Centurian!Rory there with his experiences of having already died. This is what I thought would happen, but alas! Rory and Amy were trapped aboard a crashing honeymoon cruise thing. Sadness.
(Although, ideally, Rory would be the past in my brains because we've seen that he's really attached to places and people and ideas from before and doesn't always adjust to new ones (like in the Dream Lord episode) and also, dressed as a Roman soldier. And there would be Christmassy quips about the Romans crucifying Jesus and Rory would be all- "Yeah. Well. No one's perfect." And then we'd have serious face Doctor for the future. Yep.)
The premise of the episode - the Doctor changing Scrooge!Dumbledore's life around to try and change time - is an interesting one. Interesting in that it's a rookie move for the Doctor to make because he knows that some things cannot be changed, even if you go back and try to change them deliberately, and also because it's quite full of childish arrogance. He's doesn't flaunt his ability like I imagine Ten would have done, but he doesn't seem to realize that you shouldn't actually change people like that, even if it is to make him a better person.
But then, it also felt like something the First Doctor would do and he is commonly held by his own future selves to be the wisest of the lot. He was very cleverly manipulative, often sending his companions to make friends with useful people so that they could take advantage of skill or position in order to get what he wanted.
Child!Scrooge!Dumbledore and the Doctor were fantastic, though. Love them together. With the fish and the shark sleigh and Christmassy Christmasness. Brilliant. Matt Smith should always act with children.
I love the image of a beautiful blonde woman in a white dress singing to a shark in a creepy freezer filled chamber. Possibly my favourite moment of the episode.
Also, that shark lived a damn long time with that chunk o' screwdriver in its gut. Well done.
I enjoyed the episode. It was silly and cheerful and proper Christmassy feeling and childlike, which seems odd because it didn't feel like the characters were in any danger at all except for the bit with the shark in the bedroom. Usually the specials maintain a bit of urgency and danger throughout the story (or absolute misery, like last year), but this one didn't. I don't know if I like that aspect or not, but if I don't, it didn't detract from my viewing of it all that much.
All in all, lovely.