2. This Doctor Knows That He Saved Gallifrey
BBCOne of the major reasons why this Doctor should be jollier is because he knows that he actually managed to save Gallifrey, rather than destroy it as he first thought. This controversial move will surely bring some peace to the Doctor, not only because he knows that there are other time lords out there, maybe even his family, but also because he now doesn't have the guilt of destroying his home planet and everyone on it. It made sense that Gallifreys destruction should make the Doctor slightly depressed, and this was one of the best aspects of Christopher Eccleston's Doctor. Yet even with the knowledge that he destroyed his own home, he still manages to muster up a smile now and then. This new knowledge, therefore, should put a bright spring in the Doctor's step, not make him darker. He now knows that out there somewhere is the place in which he grew up, and that one day he will find it, which leads nicely into the final reason...