It was an excellent episode and with plenty of mentions to things throughout Doctor Who history, especially NuWho. Unfortunately, /who/ considers it pretty bad as a 50th anniversary, but it gave strong evidence that Moffat wasn't yet a dried out husk.
Matt Smith announced that he was leaving because he wanted to go crash his career in Hollywood. Moffat was forced to come up with a script in a very short window of time and produce a regeneration story, Christmas special, and tie up some loose ends. It was okay, not as bad as a lot of people say but it really could have been significantly better.