Show-runner Steven Moffat said:
“The Doctor at Christmas is one of my favorite things – but this year it’s different. He’s lost Amy and Rory to the Weeping Angels, and he’s not in a good place; in fact, he’s Scrooge. He’s withdrawn from the world and no longer cares what happens to it. So when all of humanity hangs in the balance, can anyone persuade a tired and heartbroken Doctor that it’s time to return to the good fight? Enter Jenna-Louise Coleman…”
I cannot tell you how happy I am that the Doctor (Matt Smith) really suffers in the wake of the loss of his friends. Not that I’m trying to be sadistic, you understand, but such a momentous change has to have repercussions. On a show like this, Moffat easily could have picked up the story 300 years later, with the Doctor’s hearts healed from the trauma. I’m looking forward to see how the Doctor changes between now and the end of the season.