While I like to think I remain capable of critical thought on the matter, I'm an unabashed Dr Who fanboy who hasn't had his fix in awhile, so I may be biased.
I quite enjoyed this one. I've actually enjoyed Capaldi from the start, but the writing for him suffers a bit from wild mood swings between manically silly and serious. I prefer it when they write him a little more serious, and this one is squarely in the silly (like pretty much all of the Christmas specials) and yet... I think they pulled it off this time? It _is_ silly, but good-silly? The romance side-story came straight out of a Hollywood cookie-cutter, but they play it for laughs so it kind of works? And I like the hints that the Doctor is actually a bit messed up by recent events in his timeline, rather than just blithely moving on to the next companion.
So yeah; enjoyed it thoroughly.