I loved the Christmas episode! Of course, A Christmas Carol is one of my favorite stories, so I'm a little biased.
I also loved the fourth episode of Doctor Who: The Adventure games. The Vashta Nerada are very terrifying monsters, so the feeling of suspense worked much better here than in previous episodes. I also liked that the story picked up right where the last left off. I hope we get four interconnected stories next season.
On a side note, it was also interesting that both the television and video game Christmas episodes featured alien sharks. Sharks aren't the first thing that comes to mind when I think of Christmas, but in both cases, it worked.