Overall, I think that the Doctor Who team did a superb job with this anniversary story, and while there was no way that they could satisfy every fan, young and old, Steven Moffat did a creditable job of giving the fans a show that they could enjoy and celebrate about. There was something here for most fans of the series, though as a real Classic Who fan, I would have preferred to have seen more of the classic Doctors, but such would have crowded the story too much. Moffat handled that element of the story well. It was glorious to see the Tennant and Smith Doctors together, and there was some scintillating (and at times quite humourous) dialogue to the episode, but the serious moments were there as well. John Hurt's Doctor (and we can call him one now properly) was simply marvellous, but it was a wonderful treat to have all 13 Doctors involved in some manner. Having Peter Capaldi's Doctor show up, if only in intense eyes shot, was excellent.
I was pleased and surprised at Billie Piper's role in this, as she was perfect as The Moment, and the presence of Jemma Redgrave's Kate Stewart was lovely as well. Companion Clara really had little to do in this episode, as to be honest, once her big secret was revealed and solved in the last series of the show, she has become a bit mundane. But this was a story about the Doctor after all, and thus her character was shoved into the background somewhat, though her insight into the situation at the end was quite wonderful.
While the Daleks did what Daleks do in this episode, the Zygon presence here was somewhat pretty... useless, and a bit flat. They weren't the focus of the story, of course, but I do have to wonder how the negotiations resolved in the bunker facility. I loved the character of Osgood, especially with the Tom Baker-like scarf as part of her ensemble, and the moment when the Zygon copy of her gave the real one the inhaler was wonderful.
Some of my favourite moments in the episode were, in no particular order...
The scene at the very end with Matt Smith and the assembled Doctors. Brought a lump to my throat.
The opening bit with Clara driving the motorcycle right into the TARDIS.
The bit where Osgood and the other UNIT fellow had to deal with the statues. I thought they might be Weeping Angels, but was pleased to see they were Zygons.
The meeting between the Tennant and Smith Doctors. Sonic screwdriver comparisons, indeed! :)
The appearance of "Rose Tyler" and realising that it was actually The Moment.
The brilliant scene in the Time Lord War Chamber with all the various incarnations of the Doctor. Well-handled by Moffat.
The opening sequence with Clara teaching at Coal Hill High School and the beginning reminscent of the opening moments of "An Unearthly Child".
Tom Baker!! Squee!!
The sequences in the underground UNIT vault with all the DW memorabilia, and materials from the Classic series. (I wonder if someone will eventually post something mentioning all the various stuff that was there with their connection to the series' past at some point? Wouldn't be surprised.)
One of the biggest regrets that I have about the episode was that Christopher Eccleston didn't participate in the story, as I had hopes of seeing the complete regeneration from John Hurt's Doctor to the Eccleston Doctor. And there are so many questions about the outcome of what's happened with the Time Lords that... Ooh, the mind is just boggling!
Overall, in certain ways, it was one of the most enjoyable episodes of the New Who in a long time for my money. That said, I don't think it will take the place of "The Three Doctors" in my heart, for a variety of reasons.
Still, well done, Mr. Moffat!