Less to say than usual about this case. It’s a Holmes pastiche, written by an American screenwriter looking for something to do during the 1973 strike (Meyer later moved to directing; some Star Trek films are apparently his best-regarded work in that field).
Stylistically, the pastiche is more than competent, and that’s no small thing: good pastiche is hard to do. In that familiar, slightly awkward, slightly pompous Watson style, the first half of the book details the narrator’s successful scheme to get Holmes to Vienna so that Sigmund Freud can cure him of his cocaine addiction, and the second half recounts how the restored Holmes foils a vaguely improbable international conspiracy kind of thing.
The first half is, I suppose, something of a departure from the usual Conan Doyle fare, but also something of a missed opportunity. Holmes, deep in cocaine psychosis, being chased around the labyrinth of his subconscious by Freud? Yes please. A couple of overwrought hypnosis scenes and some jiggery-pokery with hidden syringes? Oh. Sigh.
The second half is straightforwardly like one of the middling Holmes stories, consisting of various stagey opportunities for him to do the whole deduction performance and a bit of derring-do in pursuit of the bad guy. Along the way, there’s plenty of reference and allusion to the canonical stories and the critical apparatus around them. I say “critical”, I think a lot of what Meyer is referring to is really closer to fan fiction avant le lettre. Anyway, some of this stuff is pedantically brought to the surface in “editorial” footnotes, more is no doubt left to be truffled out by people with their snouts deep in the Holmes humus (how’s that for stretching a metaphor just beyond breaking point). Right at the end, we do get a bit of Freud rummaging around in the recesses of Holmes’ mind, but this actually just reinforces the fanfic feeling: what emerges is mostly the sort of extra-textual biographical information over which obsessives like to obsess.
So, yeah, to the extent that you like Holmes, you’ll probably like this to more or less the same extent. Not much more to say of it than that.