Brilliant is the new Fantastic
The special was certainly a character story more than a plot story. But the character interactions and banter were excellent, and it was amusing to see them lampshade the first Doctor's 1960s chauvinism.
Really, trying to cram a denser plot into things would have almost been awkward and just cut out some of the fun bits. And honestly, I adore the sudden realisation that there's "not an evil plan".
I've seen Doctor Who described as being a rollercoaster. The fun is the ride and not the destination or anticipating the twists & turns. This episode is a good example.
I'm a fan for how they handled the return of Bill. She didn't become re-fleshed. She didn't break-up with Puddle Girl. (Heather?) They didn't pull a Clara and un-kill her. Nope, she was dead and this was just a super advanced robot with her memories
Oh, man, and when the WWI soldier revealed himself to be the Brigadier's father... all the feels. And the Christmas truce was a lovely example of how to use the season to the advantage of the story. This wasn't set at Christmas just because that's when the episode aired, but there was an actual reason.
The end was interesting. I enjoyed that Doctor Twelve didn't try to become female. Intent wasn't implied (and thus, it avoided the idea that the previous twelve rejected the idea of being female). His final speech was nice and dramatic. Some good quotable lines and wisdom, but not the heart wrenching affair that was the Doctor Ten or Doctor Eleventh's farewells. They did milk the "reveal" that he was now a she, slowly revealing the face rather than the abrupt change of past regenerations. Like you couldn't instantly tell by the eyes. There were some nice dramatic shots (the ring falling off and such) but that certainly took some time away from seeing her reaction and getting a few more lines in.
I did also note the amusing hypocrisy of having the first female Doctor be unable to drive. But, Matt Smith and Capaldi both crashed the TARDIS initially. And it makes for a fun dramatic cliffhanger without locking in the next creative to a set story or villain. (As for blowing up the TARDIS, that does give the easy out for the next team to come in and update the sets.)
The first episode of the new season could start with the Doctor falling and the TARDIS materialising below & catching them, and then moving on without a missed beat. Or it could have the Doctor land in a river, being found, and having to save the day with no TARDIS or screwdriver or potentially even knowledge of whom they are. (It also leads into a nice potential set-up of having the Companion just find the Doctor and help them, spacing out introductions to elements of the show for new viewers.)
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"Hate is always foolish; love is always wise. Always try to be nice, but never fail to be kind."
Great words to live by.