Okay, I think everything that I could say already has been said. I rewatched it, and it...well, the premise worked a bit too well. Like Sherlock, we were expecting Moriarty to pop out of the shadows at any given point, and he...well, didn't. If this episode felt wierdly anticlimactic, it's because of that. Other series had some tangential connection (particularly Scandal in Belgravia, where Moriarty loomed as a presence and background mover).
And like usual, the "fuck yeah, mary died!" responses lack taste and decency. It's not a good response to have, regardless of how much you may have disliked a character, least of all because it doesn't mean she's really gone. Now she's probably going to haunt the rest of the season, at a minimum.
And I don't really approve of her being killed off for storytelling reasons. Mary was, imo, at her best when she was helping Sherlock and John solve mysteries as they went along. Not the throwaway mysteries we were shown in this episode, but stuff like the Sign of Three episode where she remembered details Sherlock and John forgot. Instead, they circled back on her past and ended her there. I mean, this is literally what Sherlock murdered Magnussen to bury, and literally the next episode (not counting the special), here it comes back and boom, just that like, she's gone? I...don't approve.
I wasn't a big fan of Mary in general, but there was clear room for growth and improvement, and I feel this death was premature. When you have a character that people aren't too hot on, the solution is almost never to kill them.
All. that said, this wasn't a pure fridging. I feel you can kind of see through the curtains and realize that the writers just wanted John free of her, but even though I disapprove of the idea, credit where it's due, they did Mary justice by exploring her story. She didn't just die to give John and Sherlock more issues, it's her own issues that returned to haunt her.
Other stuff was just weird. John cheating is as off as anything, since all indications were that they were happy. It makes me think kind of little of John if all it takes for him to break his long fought for vows is some baby trouble. And Sherlock being that careless...I mean, this has been something of a staple since the start, but you'd think by now he'd just learn to process what people thinking on an intellectual level if not an emotional/empathetic one. What did he think would happen if he continued to piss on the angry old woman with the gun? If there is a big flaw with Sherlock's character, it's this. The writers are highly selective on when Sherlock can read a person. Because he can do it, he's done it a thousand times before either to solve a case or else crack a joke, but the moment it becomes convienent for drama (or also to crack a joke), he's all "What are these hoo-mans thinking". It's just so transparent at this point.
Overall, not one of their best. Blueballing the audience with a bait and switch moriarty (and for god sakes, just bring him back you assholes, or else we're going to have Season 8 sherlock obsessing about the dreams he's having about Moriarty that moriarty undoubtedly subliminally planted within him), to a less interesting story about Mary which ends with a death that won't truly help the show and plenty of out of character moments inbetween.