I find myself pining for the early seasons when Sherlock solved a clever murder cleverly with some dry humour and witty dialogue to string it all together instead of the bloated 'too-clever-by-half' plots, superspy characters, and ridiculous villains.
It's interesting that you say that, because I'm not sure that I'd call those elements new additions to the series. Sherlock was tangling with spies and assassins in "The Blind Banker," and "A Scandal in Belgravia," the main villain in the first two seasons was Moriarty, and they had their fair share of overly-convoluted plots.
Holy shit, "The Final Problem" was fucking horrendous. I've excused weaker episodes in the past on the grounds of the cast being good enough to make it enjoyable, but even they couldn't save this one. This was painful. This was agonizing. Nothing about it had anything to do with the
Sherlock we know and love, and none of it made any sense. Where to even fucking begin with this?
Why would Sherlock think that the best way to trick Mycroft into revealing Eurus's existence was with staging a weird horror movie-like scene?
Why would Mycroft fall for that? He knew that Eurus was an adult and supposedly imprisoned.
Wouldn't it have been so much simpler for Sherlock to talk to his own non-secretive, down-to-earth parents first? They didn't know everything, admittedly, but they could have at least confirmed Eurus's existence.
How could Eurus be controlling or programming people with her pseudo-nihilistic gibberish?
Even if we allow that her nonsense was particularly compelling or persuasive (it wasn't), how could she have control over the entire Sherrinford staff, to the degree that nobody tried to stop her during this weird scheme of hers? Did everyone there have to spend some time with her?
Why did Eurus even bother with that whole impersonation stunt in the last episode, anyway? None of it had anything to do with the plot in this one.
How did Eurus get to and from Sherrinford? Did the staff provide her with helicopter rides or something?
How did Eurus get ahold of the governor's wife?
How did Eurus get ahold of the three brothers and discover the details of their alleged crime?
How did Eurus get ahold of all her props and equipment for her scheme? The rifle, the coffin, the multiple TVs, etc.
How did Eurus bring Sherlock and John back to Sherlock's old home?
How could Eurus simply have been impersonating the girl on the plane the whole time? Even if Sherlock couldn't tell that Eurus was simply disguising her voice, wouldn't the lack of background noise (like the roar of the engines) give it away?
How does it make sense for Sherlock to replace the memories of his friend with the memories of a dog? That's just stupid.
What was the point of bringing Moriarty back for this, from an in-universe perspective? The video clips of him didn't really add anything to the intensity of Eurus's dilemmas.
How did Moriarty somehow manage to be the most sane and rational part of this episode?