To my mind, the Six Thatchers is the weakest episode since The Blind Banker. I watched it with the same feeling I get when reading fanfic that's competently written but subtly off the mark in terms of characterization and believability. It was John and Sherlock, but ever so slightly caricatured.
For instance, one of the things I enjoy about Ritchie's first Holmes flick was how it played up Sherlock's physical prowess (which although mentioned in canon I had never given much thought to) and spun a story where having that element front and center made sense. Sherlock's physicality just struck me as jarring in The Blind Banker.
I was also dissatisfied with the “ammo/amô” reveal. Sherlock's seen through trickier misdirection before; that he fails to do so here seems more like convenience plotting than a credible turn of events. Even the episode's thematic thrust (for which, see below), failed to wholly sell me on this.
Then there's Mary. Although she continues to rock as a character, there was plenty of convenience plotting for her too. For instance, the memory stick. Why on earth didn't she destroy it like the previous one in series 3?
I had two theories about how Mary would die: of tuberculosis after a failed biological attack (for some reason, that's what I feel she died of in canon) or during childbirth (as Watson isn't a parent in canon). So while her death itself wasn't a surprise, what caused it was. Even though I eye-rolled at her spending more of her dying breath on Sherlock than John, gah, her death scene was gutting. I'm sorry to see her go. She's such a great character.
The other things I really liked about the episode: the depiction of John and Mary juggling parental duties with attendance upon Sherlock was both clever and realistic. And I loved John being the stay-at-home parent because Mary is the better choice to go assist—and both she and John acknowledging it—that was excellently done.
I also thought John's affair was very well done. “I was just so stressed by parenthood.” “I just needed a boost because [my wife earns more than me/has a more prestigious title/a better career]”--these are excuses I've seen more than one man bandy about to try to justify his infidelity. And here we have John Watson, a doctor and probably used to being one of the smartest guys in the room (only Sherlock's far smarter), and a former soldier (only Mary is far better at martial stuff), and a new parent into the bargain.
It ties right into what I see as Gatiss' main theme for this episode: that your strong points will become your Achilles' heel if you aren't careful. Hence, Gatiss plays Sherlock's physical prowess and mental abilities up to the max, but in the end he can't dodge the bullet or correctly identify the antagonist. And what does John decide to do when he's surrounded by people who are better at the things he probably sees as defining him, and takes on a more traditionally feminine role as a result? It makes Mary's final act all the more meaningful, because she's the only one in the episode who's clear-eyed about what's awaiting her in Samarra.
(Final random thought that doesn't fit anywhere: I'm not the only person who noticed how they played up the make-up and lighting to make everyone look haggard and old, right?)
“The Lying Detective” finds the show back up to snuff. Yes, the social commentary on how money, fame, power, and the veneer of charity enable evil was hardly subtle, but given what's going to happen in six days' time, it sure was cathartic.
Sherlock vulnerable and adrift was a nice change from the Sherlock Stu of the previous episode; Cumberbatch is frighteningly good at portraying a manic meth-head. Toby Jones is a fantastically creepy villain and the early interactions with his daughter were nauseating.
And oh, I was so, so glad that we still have Mary with us (in a way). And Mrs Hudson! I probably scared the neighbors laughing myself silly. Mrs Hudson is perhaps my favorite character in the series.
Having said that, I have a big gripe with the way the writers have handled Rosie. Like, sure, John's a father now, but don't worry, there's a pat solution that frees him up to engage in escapades just like he did when he didn't (theoretically) have parenting responsibilities. Meanwhile Molly, from whom we've thus far seen zero indication of being anything other than as equally career-centric as the show's male characters, is left holding the childcare bag. I sense the writers thought having someone with ties to John and Mary step into the breech would be more palatable to viewers than John leaving Rosie in the care of a nursery or nanny, but all that does is beg the question as to why it isn't it Lestrade or Anderson stepping up to bat.
So we're left with John as a “father” who sidesteps the drudgery of parenting to continue the professional activities he's always engaged in but then drops in for a few hours of interaction with his kid each week. Realistic? Actually, yes, far too much so for my taste. Adding a throwaway line about how he's “not there for Rosie when she needs me” does not absolve him or the show's writers of this. (Incidentally, my speculation after the first episode was that Mrs Hudson would care for Rosie while John was out adventuring, but the writers didn't take that route. So I guess the silver lining is that I now have headcanon of John asking Mrs Hudson to do just that and her telling him exactly where to park it.)
But oh! The ghost of Mary. And how John getting into her head lets him think more like Sherlock would. And how she rivaled Sherlock's powers of foresight. And while I'm not sure how I feel about John's affair with the bus woman never becoming physical, I don't feel like it's a cop out either. And it did give us multiple instances of human vulnerability from Sherlock, which were awkward but rewarding. I am excited to see how the third episode stacks up, to say nothing of what a newly introduced character's angle is.