Having finally watched it, about all I can say was that it was passably average. The storyline(s) were incredibly hackneyed, but it's Christmas and it's DW. I agree that the lack of Amy was a bonus. The young Kazan looked like Rory to me and was a nice kid (just like little Amelia). But the rest of it was pretty much steampunk tat. Keep the punters wide eyed for an hour on Christmas Day, put a bit of emotion in there and it's all eminently forgettable.

The odd bit of "let's scare the children" stuff with the bit about the spides in the closet was typically Moffat.

Really, it was about the level I expect of DW now, although it is a one off, rather than the series with some kind of plot arc.

I don't think I could be bothered to watch it again.