OK, I’ll keep this spoiler-free for now, but some kind of comment seems necessary…
Lots of Good Stuff. We learn more about the Time War, and why the Doctor did what he did. We learn why the Master has been hearing that drumming noise in his head all his life. We manage not to learn who one apparently important person is.
And we finally learn who is going to knock four times. And it might not be who you were expecting.
And we have a final goodbye from the Tenth Doctor to his friends.
And the Eleventh Doctor makes his appearance and based on about twenty seconds of post-regeneration confusion, he looks like he’s going to be interesting…
I’ll probably need to watch the whole thing a few more times, but overall it was a fitting send-off for a truly wonderful Doctor.