There are spoilers contained within this review, so be warned.
First off, let it never be said that Steven Moffat is a man who is unafraid to take chances with Doctor Who. Love him, hate him, or just be thoroughly confused by him, he is not afraid of the change that is so very vital to the legacy of the show. He's given The Doctor a wife. He's created a whole new incarnation to help tell the greatest untold story in the mythos. He canonized the Big Finish audio dramas (At least regarding the Eighth Doctor). It would be impossible and ungrateful to not respect that.
However, a big problem with the Moffat era of the show is not what he does but how he does it. Nothing really sums that up better than "Death in Heaven", the season finale to one of the most divisive seasons in the revived show. Was it good? Yes, I'd say it was good. I was moved, but it was also a mess, and a mess that left far too much of the magic behind the curtain on display.
Apparently it's true, and The Master is now The Mistress. Michelle Gomez simply eats every single inch of scenery she dances through. Even Peter Capaldi, no lightweight in the thespian arts, seemed to have difficulty keeping up with mad rhetoric and unabashed evil. There hasn't been a villain so sincerely hammy and happily dastardly since Raul Julia played M. Bison. She is clearly having an obscenely good time, and they even brought back the ridiculous but hilarious tissue compression eliminator. A good bad guy needs a stupid laser just like a good hero needs a magic wand or an enchanted sword.
The decision to introduce a switched gender to a main Time Lord character like The Master is daring, but it comes with hang-ups that I never saw considered when the discussion about a possible female Doctor were swirling last year. Eager as I am to see that one day, Missy made me grateful that it didn't occur under the current regime.
There's always been something of a crazed, jilted stalker in The Master's relationship with The Doctor. You can go all the way back to the way they converse in "Claws of Axos" and read a subtext there, and it got even more glaring in modern years with Eric Roberts and John Simm. It's very much like the relationship Joker thinks he has with Batman, and slip that comparison into your pocket for a minute because we're going to come back to it.
However, it is extremely bothersome that this masterful Mistress embodied in Gomez has her motivations completely reduced to a twisted form of affection for The Doctor. Her entire plot, from the murder of his friend in a kind of petty jealousy to the army of Cybermen she creates, has absolutely nothing to do with herself at all and everything to do with how she is perceived by The Doctor. For as loud and wonderful as she is there is never a single second that gives her a character motivation all her own. She has literally traveled through earth's entire history working on a plot where the end game is an appeal to The Doctor that they are more alike than he thought and maybe they should run away together.
This story continues on the next page.