Now that was a nicely suitable Christmas edition. After all the stress and trauma of the last three episodes, it was nice for the Doctor to have a more traditional romp, with the added bonus of the return of River Song.
Given their slightly complicated, wibbly-wobbly, timey-wimey history, it’s not altogether surprising that River takes a little while to realise who this absurd character with the attack eyebrows is, which leads to more fun and games. There is, of course, a Terrible Threat to be dealt with, complete with a MacGuffin that ends up having a useful purpose beyond being shiny.
The Doctor fulfills a promise, and gives River a present that we first saw a long time ago, solving one remaining question from way back when, and we actually have a happy ending, which is something the Doctor’s been overdue for.
 Sometimes I think Mr Moffat plans all this stuff very carefully, other times, I think he remembers something he did years ago and decides to use it again. Damned if I know which one it was this time.