I don't know how to feel about the Missy reveal, tbh. On one hand, it now establishes that Time Lords can regenerate as any gender they like and that not having done so in the past doesn't mean they never will; so all fan talk about "it would ruin the show's continuity!!" or "that line about the Corsair was just a joke!" is now proven to be as ridiculous as it always was. On the other, she is now just another one of "Moffat's Gals" and, yeah, that's not really what I wanted for the character
I also strongly disagree with certain critics I've seen saying that this is the only time the Cybermen have been done well since the show's revival. No it isn't.