Must have been a mixed blessing for Matt Smith that the end of his tenure as the Doctor was filled with so many milestones for the series--the 50th anniversary, the 800th episode, the onset of a new cycle of regenerations. Because as awesome as it is to be the actor present for these big moments, it also means giving up some of the spotlight at a time when everyone should be celebrating you. Fortunately, the show was lucky that their lead actor has been nothing but humble as well as superbly talented enough to handle everything thrown at him. And boy did the show throw him a lot...
Starting at the end first, the Christmas special "The Time of the Doctor" was literally a buffet of all the hanging plot-lines that Steven Moffat created during his tenure as the show-runner. Now that "his" Doctor is leaving, he may have felt he needed to address them all, but even with the extended running time the explanations to the Silence, "Silence Will Fall," Trenzalore, crack in the fabric of spacetime, "Doctor Who?," etc., just felt simultaneously rushed and convoluted dragging most of the episode down. Not that I didn't appreciate them trying to explain literally everything, but a little mystery would've worked. The one plot point decision I was fine with was the regeneration cycle reset even though I still felt the execution of it was badly handled mostly due to the muddled and confusing motivations of the Time Lords.
With all of that said, Smith, even hampered by hilariously bad old-man make up for the latter half, was fantastic. He hit all of the emotional beats just right, echoing David Tennant's ability to cut through all of the bullshit in his last episode as well. The hundreds-year long siege of Trenzalore seemed as half-baked an idea as a lot of Moffat's ideas the past few years and yet there was something quite affecting seeing the Doctor stay in one place for so long (too bad we only get a montage and a time jump). Eleven's scenes with Handles (seemingly a more realized companion than Clara at this point) and his touching monologues reflecting the end are highlights as was the surprise cameo of Karen Gillan in the form of Eleven's first companion Amy Pond. A solid final episode in terms of acting from Matt, but everything else left much to be desired.
Fortunately the 50th Anniversary "The Day of the Doctor" was much more successful even with a plot that was seemingly as convoluted. It all revolved around the Time War, a universally devastating war between Daleks and Time Lords, that forced the Doctor who kill his own people for the sake of saving the universe. This war launched "New Who" and had only been revisited a few times indirectly until this episode. John Hurt played the War Doctor, a regeneration that came after Eight and before Nine. In his quest to end the war, he encountered his future selves played by Tennant and Smith. Smith was masterful here never relinquishing the lead, but always giving the others the spotlight as needed. Plus his chemistry with Tennant, as expected, was crazy good. Clara was again slightly a bit incidental to the whole thing (hoping more for her as Peter Capaldi's companion), but their decision to make Billie Piper not play Rose was inspired. Though my dream scenario would've been for The Moment to have been played by different companions, no matter how logistically impossible it would have been in real life.
The episode was chock full of homage to Classic Who complete with a surprise cameo of Tom Baker and it all seemed to work organically. Even the big polarizing reveal that the Doctor didn't really kill his own people trapping them only in an alternate universe was fine by me since I don't think that really took away to the emotional journeys taken by Nine and Ten and opened lot of possibilities moving forward (then again how they were used in the Christmas episode gave me pause). The only thing I didn't like about the episode was how lame the Time War looked. As my friend brought up, it looked Star Wars-lite. And why did it seem like the war was only being fought between the Daleks and the Time Lords on Gallifrey? What made the Time War so devastating was how wide-ranging its impact was to the entire universe. In all, I still found it quite good especially with the lower expectations I've had for Moffat.
But to end this long-winded post, I want to bring it back to Matt Smith who was the youngest actor to ever play the Doctor. His physicality, his penchant for hats, his impossible hair, his cool bow ties, and his ability to exude age old wisdom will all be missed. Geronimo!