Has a TV show ever paid such close attention to its fans?
After much internet buzz that Matt Smith could not be the Doctor in the Xmas special because he had cut his famous mop while filming a movie, the scriptwriters shaved his head and put him in a wig. Hard to believe that during months of speculation, that simple little solution didn't seem obvious.
They also settled the question of regeneration. We knew they would; Dr. Who is far to valuable a franchise to kill off simply because long-established canon says you're on your last face of Doctor; but it's nice to see that they cared about it enough to dedicate an entire conversation where the Doctor counts up all of the past events.
It was, however, a bit much that the excess energy from this regeneration was apparently sufficient to destroy a Dalek battleship. For the man who almost never fires a weapon (during this episode devoted to a long war the only direct kill we see him make is convincing a Cyberman to shoot himself) it was a dangerous precedent. But of course, that Doctor is gone now, and the scriptwriters get another chance to create rules and limitations they can then dramatically break later down the line.