Before I get to discussing the plot of the episode, I must first mention Capaldi's performance. As with any Doctor's inaugural episode, his freshly regenerated self is always at his zaniest. (Regeneration is a dodgy process, after all.) This is a well-established element of the show and is to be expected; however, it does make it difficult to gauge the new Doctor within his first episode. So, while I have not been amazed by the Twelfth Doctor yet, I am sure I will be in the new future as soon as he develops.
Speaking of regeneration, I understand that there needs to be exposition to explain the process for new viewers; however, it was completely mishandled in this episode. This task is usually given to the companion, and as he or she learns about it, so does the audience. That normally makes sense, except for the fact that this time the companion already understands it completely. Clara has already met all of the previous Doctors on two separate occasions (“The Name of the Doctor” and “The Day of the Doctor”)—the Twelfth Doctor's eyes even showed up to help! Yet, she has trouble accepting that her Doctor could change. This leaves Madame Vastra, Jenny, and Strax to explain things to her; despite the fact that up until this point there has never been any indication that they have knowledge on regeneration. The episode would have made much more sense if Clara explained things to the trio, instead of the other way around.
The advertisements for Series 8 have been touting that it will be a bold, new direction, which seemed strange to initiate that with a sub-par rehashing of old ideas. Turning the Doctor darker and Clara's subsequent distrust of him feel far too much like the Sixth Doctor and his relationship with Peri. Although, this time around it does not work quite as well. Taking the Doctor in a darker direction is a fantastic idea and while it has been done before, there is still much that can be mined from it. The major problem with it now is a matter of timing. The Doctor ponders his past mistakes, leaving him and Clara to wonder if he is actually a good man despite the fact that he just atoned for his greatest regret and managed to save Gallifrey. That was two episodes ago, and yet he cannot help feeling mopey for some inexplicable reason.
A major flaw of the episode is the return of the clockwork droids, or rather, not the return of the same clockwork droids but other ones that commit the same offense. Back in Series 2 Steven Moffat wrote “The Girl in the Fireplace,” which was fantastic. In that episode the robots aboard the spaceship SS Madame de Pompadour went insane and took to a murder spree, killing the crew and using their body parts to repair the ship. In this episode the robots aboard the spaceship SS Marie Antoinette (sister ship to the former ship) went insane and took to a murder spree, killing the crew and using their body parts to repair the ship. Imagine, if you will, how obnoxious it would have been if for Star Trek II the crew of the Enterprise stumbled upon another Voyager space probe and it also became sentient. Instead, they met up with Khan and incurred his wrath in one of the best sequels ever. Worse than the lazy writing is that this means that somewhere in the universe is a negligent corporation building murdering robots who are prone to insanity and there appears to be no sort of recall in order. Even the “Don't breath” lines felt like Moffat just trying to replicate his “Don't blink” catchphrase.
As far as I am concerned, the biggest offense of the episode is the phone call. Typically, at the end of a new Doctor's episode, he has an “I am the Doctor” moment which usually involves some sort of speech explaining that he is still the same man. In what could only be described as pandering to fangirls, Matt Smith shows up to deliver this speech instead of Capaldi. (I would like to state that this is in no way a dig at fangirls, but rather, it is directed at those involved in making this decision and their illogical reasoning that makes them think that fangirls will stop watching the show now that the Doctor is no longer young and cute.) Capaldi was robbed of an integral moment in the evolution of the character. Bringing back the Eleventh Doctor also goes against one of the central themes of the show. Throughout the show's fifty year run, there has been a thread of accepting loss and moving on. Having the previous incarnation attempt to help win over the audience for the new one is not moving forward, it is backpedaling, and instead of giving the Doctor more credibility it loses some. He should earn it on his own, not rely on a past actor's credibility.