The urge to indulge in long goodbyes proved too hard for Steven Moffat and Peter Capaldi and so we all got a Christmas special heavy on farewells. I wish they wouldn’t do this, it didn’t work for David Tennant and as much as I like Peter Capaldi, he’s had a shorter tenure and less impact on shaping the new version of the Doctor as a character. Aside from anything else, it has been a long-established character trait of the Doctor that he does his utmost to avoid long goodbyes.
Still, this was an episode that wasn’t short of ideas, jokes, references to old episodes and cameos but very short of a plot. David Bradley reprised his impersonation of the First Doctor that he’d deployed as William Hartnell in An Adventure in Time and Space to great effect. Pearl Mackie got another send-off as Bill Potts but no hint that she might reappear in the next series (no hint that she wouldn’t either).
I’d still would have preferred less obvious sentimentality and more story though.