I'm sorry that this ends up being my first review honestly. I'm not just a hater I promise.

The st4rshiptr00per household agrees: bloated, too many ideas being introduced while other, previous, interesting ones are dropped unceremoniously -- and the whole Timeless Child concept completely overshadows the Doctor's character as someone whose superpower is being inhumanly Humane and loving, and reduces them to simply The Chosen One. An absolutely buckwild decision to make with a beloved character who contained infinite possibility. All mystery is removed, and all their importance is now due to them being The Big Magic Guy. And for the record: I also hate this being done in the Cartmell Master Plan. I simply do not think this should be done to the Doctor.

Goodbye to the Lone Cyberman I guess, thought that guy was interesting and important but were TCE-ing him away now.

I continue to be put off by the Doctor/Master dynamic in this era. Other people have complained about Spymaster feeling completely disconnected from Missy and how her character arc ended, but I'd go further and say that Thirteen's feelings towards him feel jarring as well. All previous modern-Who Doctor/Master dynamics have been very clear on the Doctor still having some love for the Master that puts them in conflict with their companions who only see the Master as a supervillain. But Thirteen seems to just outright hate him, and the Spymaster is only slightly less vicious about it than she is. I feel terrible for Sascha Dhawan. I want so badly to like his character -- I love his scenery-chewing, and I can perfectly envision him doing spectacularly with a more complicated, dramatic, romantically-tinged Doctor/Master dynamic like we've had previously, but the way the two of them are written in this past season is so lacking.

Note: I have seen the theories about the Spymaster actually being the regeneration between Simm!Master and Missy, and I think it's a bad sign if your audience has to come up with an unsupported conspiracy theory to make your characterization make sense. I've also seen this turn from Missy to Spy described as a "relapse", which is slightly more compelling. However if that was the case I'd want to see that actually addressed by canon. Also, the concept of a semi-ex-villain suddenly relapsing to a full on world-destroying supervillain was done infinitely more artfully in Dragon Ball Z with Vegeta's Majin arc, something I would much rather have watched, frankly.

Across the board: I have not enjoyed what this era's writers have done with the main cast, and this episode is just another low point of several this season for me.
[INSERT ANY MAIN CAST ACTOR'S NAME HERE], baby, I'm so sorry about what these doofuses did to you. You deserved better.