Well that's another one over (Christmas specials, that is.) I'm not sure yet what I think of The Return of Doctor Mysterio, having only seen it once so far.
On the plus side, it has returned to the Russell T Davies approach of a pastiche of a popular holiday blockbuster film (see The Christmas Invasion and Voyage of the Damned) rather than visiting yet another alien planet of the Dickensian Christmas people (see A Christmas Carol, Time of the Doctor and The Husbands of River Song.) On the negative side, I'm not a great fan of superhero movies.
Another good point is that Matt Lucas' Nardole was considerably less annoying than I had anticipated. In fact, I found myself looking forward to his appearances. I was less pleased to see the reappearance of the aliens with the zip-up heads and gloopy brains. I think that they are uncalled-for when the nation is digesting its Christmas dinner.
I'll need to see it again a few times to come to a final conclusion, but I watched The Christmas Invasion again afterwards, and I can exclusively reveal that it is still number one.