2016's Doctor Who Christmas special was... unoffensive and bland. There were a few things that I enjoyed while watching, a few things I didn't enjoy, and when it ended I pretty much forgot it all instantly. Not exactly a masterpiece.
Cons:
Like I said, this whole thing was pretty bland. There was a slight connection to last year's Christmas special, as we learn that the Doctor and River have just had their final "date," lasting many years. Ostensibly, this is the Doctor's first real foray out into the world since River left him to go die in the Library. That's a nice little connection, but the story doesn't really play up on it very much. Same can be said for the Doctor's sort-of companion, Nardole, who was the head of the Hydroflax last we saw him. The Doctor keeps him around because he's afraid he'll be lonely. An interesting conceit, but it's not handled as skillfully as the 11th Doctor's love for his Cyberman head, and we don't get enough time to really parse this out. Nardole's presence ends up feeling like a buildup to whatever his character will be in Series Ten, instead of a proper piece of this episode itself.
Then there's the disconnect between the stuff happening with the Doctor, and the stuff happening with the superhero. Grant was a young boy when he met the Doctor for the first time and inadvertently swallowed a powerful gemstone, giving the superhero-obsessed little boy the superpowers he always wanted. Years later, Grant is posing as a nanny for the child of a woman he's been pining for all his life. This woman, a reporter, is smitten by the mysterious "Ghost," who is of course Grant's alter-ego. You can't get much more cliche. It's the stereotypical superhero story in every way, without even a bit of nuance to change things up. Grant is Superman, complete with a glasses-wearing unassuming alternate personality. And Lucy is Lois Lane, down to the fact that she's a nosy reporter who, despite being portrayed as quite intelligent, is blinded by her smitten feelings for the superhero she's trying to investigate. Ugh. Stop.