"The Time of The Doctor" is the 2013 Doctor Who Christmas Special. It starred Matt Smith as The Eleventh Doctor and Jenna-Louise Coleman as Clara Oswald. It was the final episode of Series 7, and the final episode of Matt Smith's doctor.
If you have been keeping up with Doctor Who and the mysteries presented in it, Steven Moffat, the showrunner and head writer of Doctor Who, has been building complicated, convoluted and multilayered plot arcs since he took over at the beginning of Series 5. Each series had a cosmic cataclysm as the final episode, but each one left a few plot strings hanging, mysteriously hinted to be resolved later.
In Great Britain, the Doctor Who Christmas special is seen as something of a family tradition, where families get together and watch Doctor Who. For American audiences, where the show is more of a niche interest, the big draw was trying to find out the conclusion of the secrets that had been dropped for the past three years.
Both audiences were probably disappointed by this episode. The Doctor gets a secret message, which draws him to a tiny planet with a single town: a town called Christmas. The planet is the source of a message that has also drawn Daleks, Cybermen and Sontarans. The planet has a mystery that threatens to destroy the cosmos, and the Doctor must defend it. So he stays there, for hundreds of years of his time, defending the people of the town from invasion. While doing so, most of the plot arc of the last few seasons is resolved, as well as revealing the newest regeneration of The Doctor.
The problem is that so much has been built up over the last few seasons, that the revelations in this episode came as a disappointment. The episode was both crowded, because so much had to be explained, and also rushed, because the explanations seem forced instead of coming naturally. The hardcore fans who had been keeping track of continuity would be disappointed by the handwaving, while the casual viewers would probably be mystified.
This episode was in some ways a victim of the show's success: viewers had been built up with so much escalating mysteries that the final revelation couldn't live up to expectations. While everyone gives good performances (and the minute of screentime Peter Capaldi, The 12th Doctor, gets, is promising) and there are a few clever and exciting scenes, overall, I found the Christmas special a disappointment.