Well, let's get the elephant in the room out of the way first. There's some specific aspects of this production that I really didn't like, and was never going to. As such I'm just going to move straight on from them, because ultimately for the majority of viewers it's not going to be an issue. It created a lot of little niggles for me, but I won't dwell on it here.
As for the episode itself...I found it seemed like a non-event, to be honest. The original Doctor being afraid to regenerate makes sense, but the twelfth's decision seemed to have changed from the last story - now he wants a rest, though bizarrely he wants a rest by dying. Couldn't he just regenerate and go into retirement?
I had a lot of questions about this story, to be honest, and most of them seemed to be the obvious - why didn't Bill just say who she was from the outset? Why were the Testimony so coy about everything? At the end of the day, the entire story could have been resolved simply by the Testimony saying what was going on, avoiding the trip to Rusty and the Doctor coming to the conclusion that everything was fine.
But furthermore...surely the Doctor's actions altered time, which was something the Testimony were actively avoiding doing. Were they not upset that the Doctor had changed time? Why did Bill not bother to mention this? Did the Doctor not, therefore, change the Brigadier's timeline? Truthfully, the more I think about the story, the less it adds up.
Touching on performances, Capaldi was on fine form, as usual, though in truth his last speech in the TARDIS seemed forced, and despite the promise of an emotional farewell, I wasn't really moved in the same way I was when Matt Smith left; that regeneration seemed much more emotional to me. Pearl Mackie was fantastic (and the two cameos at the end were delightful), while Mark Gatiss turned in a very nice performance indeed.
The problem with regeneration stories, though, is that the regeneration hangs over the episode. If the story isn't firing (as this one really wasn't), there's an eagerness to get to the change. When it comes, when we get to see Jodie for the first time, she instantly makes a mark, and what happens to her immediately after is exciting and interesting; I really don't want to wait nine months to see her in action. Also...she really suits Capaldi's costume.
But if I was honest, the twelfth Doctor left with a whimper rather than a shout, which was sadly low key for such a brilliant Doctor. Too much of the story happened in order for story to happen, rather than out of any common sense reason. A disappointing end.