Short version:
loved the timey-wimey bits; not so sure about the shark.
That said,
if I read the special as the mash-up of Dickens and Peter Pan that it clearly is--with the Doctor as an inadvertent Captain Hook as well as Peter Pan flying into the nursery--then the shark makes more sense to me. (And I loved that shot of the Doctor framed by the window, longing to be let in by Kazran.) And I did quite like the way the episode handled the "Christmas future" bit, with the Doctor showing the little boy the future man he'd become--I wasn't expecting it, and I found it quite moving. Time travel ftw.
And I liked that for all that little-boy-Kazran (whom I adored) has clearly imprinted on Eleven, like Amy but unlike with Amy, the Doctor manages to be properly there this time (little Kazran has a fez! bless), it's Abigail who lives like the Doctor, in brief stopovers while everyone else is on the slow path. "I'll see you in a minute--I mean, in a year," the Doctor says, and Abigail could say the same.
Also, I might have seal-clapped when I saw Arthur Darvill's name in the credits, causing my mother to look at me like I was nuts. Maybe. Also--the Ponds and costumes: clearly A Thing.
I may have more to say about the episode (and the trailer, OMG) once: a) my finger stops hurting, ouch--I don't know quite what I did to it; and b) I've had a chance to watch it again.