I quite enjoyed the episode. I have given up hoping for better writing, but its still fun - just no point over-thinking the storylines. Capaldi has kept me watching this series.
I liked Tennant's doctor a lot (and I suspect he will always be 'my' doctor because he was the doctor when I was a teenager) but he is a completely different character and Capaldi is simply brilliant in the role he has carved for himself. I have even come to dislike Clara slightly less over this season.
Last weeks episode (Heaven Sent), although simple, was really up there for me - best of recent times. Capaldi in his element.
River's character is fun, but I think the Christmas episode might be stretching in to the realms of over-using her. The last few Christmas episodes have been appalling and I am not going to be making any special time to sit and watch it this year.