I felt like Missy was sort of... I dunno. After Dark Water/Death In Heaven, I guess they didn't have much room for improvement, but it felt like she slipped down a few notches. And the whole, "Yeah, I died, but whatevs, fags!" (not her exact words) felt just plain lazy. Obviously, the biggest apparent hole -- the Doctor going back to Skaro to point the gun at young Davros despite lack of TARDIS and the only one with a Vortex Manipulator getting vaporized -- will be explained in the next episode (or if it's a longer arc, by the end of said arc).
(I would have said SPOILERS! but for two things: If people are reading this, I assume they've already seen the episode, and also I'm not Alex Kingston, she of the Q-tip hair and the nice rack.)