So, formulating thoughts: Overall that was an excellent episode. Wonderful acting, of course, particularly brilliant performances by Capaldi and Coleman, but the two guest stars did well as well. Williams surprised me, as I thought she was absolutely pap in her first two appearances, but she puts in a much more understated performance here to the point where perhaps I wonder if she wasn't instructed by the Director to play it down a bit to not deflect any attention from Coleman for what I do believe will be her final chronological scenes as a living character - though she will, of course, show up over the next two weeks, I have no doubt.
As far as constructive criticisms go -- I think my main problem with the "reckless Clara" and the "Clara becoming the Doctor" arc is that I can't think of too many instances in the past nine episodes before this one (or even before that) of her really being like that; there's certainly been nothing quite as obvious as when the same sort of thing happened to Rose, with her and the Doctor being gut-wrenchingly unbearable in stories like The Idiot's Lantern and The Impossible Planet and of course throughout Doomsday; it felt a lot more like Rose had earned her punishment than Clara, basically.
I can think of a single way I'd change the entire series for the better in this regard; make Ashildr Clara's mistake. Rather than the Doctor use that 'medkit' on her to bring her back to life, have Clara do it behind his back. Have her cross that line, and then in turn have Ashildr be her ultimate undoing, albeit by mistake. As it is, it never really felt like she truly crossed the line, I never had that moment where I was like "she's too far gone, they NEED to be separated" as with Rose - and I use that comparison as Martha, Donna and Amy never really went that way, any of them. Martha never got the chance, Donna was too good to end up that way (but in a sense accidentally overstepped the mark in a different way altogether in absorbing the Doctor's knowledge) and Amy had Rory to keep her grounded.
