Heads up, this one is long and chock full of spoilers below the cut. TL;DR – As a long-time BBC Sherlock fan, I am disappointed with Season 4.
I will say upfront that I was able to largely enjoy each episode of Season 4 as I was watching it. The acting was still excellent, and there were certainly scenes and parts of episodes that were fantastic. But once I had seen them all and had a chance to step back and look at the season as a whole, I had more and more problems with it. Ultimately, I am disappointed in the writers for not really living up to their own standards, which they set quite high during the first three seasons.
To be honest, I was worried about this season from the moment that Moffat and Gatiss started making public comments that season 4 was going to be especially “dark.” My worries were not unfounded. Let me see if I can articulate what I mean.