I confess that I loved it, in a way I didn't love The Six Thatchers The plot's a bit ropey, but Moffatt quite cleverly used it to excavate the characters' being forced to confront their own inner demons. Sherlock as addict worked for me here, even as he gave himself over to his addiction to pay some of his debt to Mary (and let go of his sobriety at the same time).
Some of the ropiness is, I think, the fact that this season instead of subverting the Conan Doyle stories, they're using them as frames, but telling them straight--not true in prior series, where die hard Holmesians get jiu-jitsued by Moffatt and Gatiss using our knowledge of the stories against us. But this retelling of The Dying Detective is actually pretty close to the original.
What makes it worthwhile are the beats between John and Sherlock, especially after Culverton Smith begins his interminable confession. John's passionate anger at Sherlock refusing to accept and act on his attraction to Irene Adler, swiftly followed by John's confession to Sherlock and Mary of his faithlessness to Mary (Amanda Abbingdon plays Mary's response perfectly), and then Sherlock's embrace of John--it's as close as this show comes to Holmes's reaction to Watson's getting shot in The Three Garridebs:
You're not hurt, Watson? For God's sake, say that you are not hurt!'And, just as Gatiss's script from the Hounds of Baskerville was an improved version of his PROBE script Unnatural Selection (no, really) so too in the cliffhanger, Moffatt here reworks his cliffhanger ending from Jekyll.
It was worth a wound -- it was worth many wounds -- to know the depth of loyalty and love which lay behind that cold mask. The clear, hard eyes were dimmed for a moment, and the firm lips were shaking. For the one and only time I caught a glimpse of a great heart as well as of a great brain.