As always with anything written by Stephen Moffat, the episode was a mixed bag and inconsistent, yet this time the good outweighed the bad. I'll do straight away with the bad parts so as to get them out of the way. WARNING! Spoilers abound!
THE BAD:
The metamorphic Zygons have invaded Elizabethan England circa 1562, yet the queen somehow manages to keep her head and spout off knowledge of the aliens she really shouldn't have. Why the hell is this? Seriously? Moffat, I know you like to pull things out of your ass, but really, this is too much even for you.
The 10th Doctor (David Tennant) states his age as being 904, but this episode takes place from his perspective after "The Waters of Mars" and just before "The End of Time", wherein he gives his age as 906. He was 904 or 905 by the time of "Journey's End", and presumably about a year passed between "The Waters of Mars" and "The End of Time". Moffat uses a scene featuring the War Doctor, played by the legendary John Hurt, in a cell with Ten and Eleven (Matt Smith) to explain that the Doctor actually doesn't bother keeping track of his actual age and just tosses out whatever number he feels like giving, or that feels about right to him. Yes, the Doctor lies about his age, but this is really just too confusing for the audience. Consistency, Moffat. Learn it.
The Zygons have infiltrated UNIT's Black Vault archive, which houses alien technology gathered over the years, and the Doctors use a memory-wiping system installed to keep visitors from remembering their forays into the vault to resolve a deadly standoff between humans and Zygons, yet this subplot is left unresolved — as usual with Moffat, he brings something up and then forgets about it. Dammit, Moffat!
THE GOOD:
Those and other writing inconsistencies aside, there was plenty in this episode to enjoy. The subplot with the Zygons was actually fairly clever in that it offered a way out of the Time War for Gallifrey and the Time Lords: they stole Time Lord technology that freezes moments in time in the form of three-dimensional portal-"paintings", which the Zygons use to place themselves in a form of temporal stasis. This plays out later when the time comes to save the day.
The concept of the Moment, a weapon so powerful it not only achieved full sentience, but a conscience as well, was genius. It doesn't want to massacre an entire galaxy, which is what would have happened had it been used. Instead, it takes the form of Rose Tyler in her Bad Wolf persona to bring the War Doctor, Ten, and Eleven together so the former can see the guilt carried by his future selves. In this fashion the Moment hopes to change history for the better. Ever since Russell T. Davies killed off the Time Lords at the revival of Doctor Who in 2005, we fans have been clamoring for their return, only to be teased and ultimately denied by both Davies and Moffat. But this now brings up at least the possibility of a more permanent return.
All the Doctors working together to save Gallifrey.
The acting was superb all around. Plenty of humor to offset the drama (Tennant keeps mistaking real people and animals for Zygons, and the banter between him, Smith, and Hurt was priceless).
A last-minute appearance by Tom Baker, who reveals the survival of Gallifrey and the Time Lords to Matt Smith's Doctor, who exits the TARDIS to stand with all his previous selves.
SNAPSHOTS:
Here are some screen captures from the episode.
