Well, Moffat's gonna Moffat. Nah, I don't mean to sound so harsh, this is a fun and enjoyable episode, though the Moffat tropes sure were on full display. Timey-wimey hijinks, check. Characters becoming digital ghosts after they die, check. Characters only becoming sort of dead, check. The tragic fate of Joy's mother getting a more positive spin by the end, check. Granted, it is Christmas, so I can't fault the decision to go with something positive and uplifting. But it is a well worn Moffat trope, and I personally found it completely predictable. Well, sort of, at first I thought Joy's mother would somehow be saved, but then once the scene with her was set at the end, I knew they'd have her join the Joy Star. Which, yeah, Christmas, better to be positive and uplifting, I guess.
And speaking of obvious and predictable, Bethlehem could be seen coming at least ten minutes out.
But enough of my bitching. The dialogue, specifically the snappy one-liners were on fire in this episode and I will agree with the above sentiment that the Doctor stuck on Earth of an entire year as well as his developing friendship with Anita could have easily been its own episode.