(Part 1, Part 2 — incidentally, Part 2 has a lot of excellent comments which I’ve not had a chance to reply to yet — I’m well enough to write or to reply to comments, but not really both. )
So, if the Sherlock Holmes stories aren’t about Holmes himself, what are they actually about?
Well, in large part they’re Gothic stories. I haven’t gone through all the stories and counted how often each element occurs, but there’s a sort of ur-Holmes story, which goes something as follows:
Holmes and Watson are sat at home, when a woman comes to them with a problem. The woman lives in a secluded, inaccessible place, and has some kind of male protector — a father, brother, or husband, but is otherwise cut off from anyone who might help her. The male protector, who has a mysterious past that he won’t talk about, has been acting strangely recently, and making seemingly-arbitrary requests of her, and she doesn’t know why. Seemingly supernatural events have been happening, usually involving a large or exotic animal of some description, and there’s also been a man with a grotesque appearance like a twisted lip or red hair hanging around. Holmes then figures out either that the male protector plans to kill his client before she inherits the money that she will come into when she turns thirty/marries, and that the grotesque man is really the male protector; or that the male protector is being blackmailed by his evil associates from his past life, and is desperately trying to hide this from the woman.
(In just The Adventures of Sherlock Holmes, a single short-story collection, that summary more or less works for The Adventure of the Copper Beeches, A Case of Identity, and The Adventure of the Speckled Band, and elements of it appear in several more of the stories.)
What we really have, in short, is a Gothic story, in which Holmes acts as a deus ex machina to provide, most of the time, a happy ending, and also to allow us to believe in the seemingly supernatural while giving it a rational explanation (and that wish for rational-supernaturalism is, of course, the same wish that drove Doyle himself to become a Spiritualist). The stories are magic tricks, that most Victorian of artforms, and Holmes appears at the end to show you that you’ve been fooled, like saying “is this your card?”.
No, it’s not Holmes who changes in the course of the story, it’s his clients. And many of those clients are women. In fact, the Holmes stories are often curiously feminist. This may seem strange given that Conan Doyle opposed giving women the vote, but in other ways Doyle was very sympathetic to women’s rights. In particular, he supported a reform of the divorce laws, which at the time he was writing the most well-known Holmes stories said that a man could divorce his wife for adultery, while for a woman to divorce her husband she had to prove physical violence or desertion as well as adultery.
When seen in this light, the stories often seem to have an almost propagandistic aspect to them — a lot of the time they’re about women gaining financial independence and being able to escape the control of abusive men, and the men resenting that and wanting to prevent it.
And this gets lost when one looks at the stories purely through the lens of Holmes, with fairly horrifying results, like this quote from an article I’m not going to link to, titled the 50 sexiest literary villains:
Irene Adler, The Complete Adventures of Sherlock Holmes
One of the only people to have ever bested Sherlock Holmes, and (if you can believe him, at least) the only woman to match him. In modern adaptations, Adler is often portrayed as a love interest for Holmes, but in the books, she’s always working against him — sexily.
This is what happens when you have to have everything centre around the (white, male) hero and turn him into the protagonist. In the book (singular, Adler appears in only one story) Adler is not a “villain” at all — she’s a woman trying to live her own life, and not bothering anyone at all, whose arsehole ex hires Holmes to steal some of her property (a photo of the two of them). Adler barely interacts with Holmes at all, and then only because he forces himself into her life. She is never seen to treat anyone with anything less than kindness, decency, and respect. And yes, she gets her own way against Holmes, but “her own way” consists only of getting away from him so he won’t keep stalking her in different disguises and trying to steal her stuff. It’s the standard Holmes story above, except here instead of solving the problem, Holmes is the man with the grotesque appearance (he even goes in disguise, as the villains in the other stories often do).
And that’s not me putting a humorous slant on the story — that *is* the story, and Holmes himself refuses to shake his (male) client’s hand, and considers Adler by far the better person, by the end of the story. Even though A Scandal In Bohemia is one of the stories in which Holmes plays a more active role than most, and in which Holmes actually undergoes a change (going from thinking all women are stupid to admiring at least one), he is not the protagonist of the story — he is, in fact, a pawn of the villain.
But if we are forced to see the story as being “about” Holmes, to see him (or the Holmes-Watson duo) as being the character around which all else revolves, then he obviously can’t be a henchman, he has to be the hero, and so Adler has to be the villain, and we get an absurd, laughable, misreading, one which turns the story from being about a powerful man unjustly trying to destroy the life of a blameless woman for his own convenience, into one about… well, *about* nothing at all, except “sexiness” apparently. And so over and over again we get Baring-Gould types insisting that Adler must have been Holmes’ lover, and novels about how she was “really” a safe-cracking thief, and TV shows in which she’s a dominatrix, and basically anything other than the story that Doyle originally told, about an innocent woman being pursued by powerful men and managing, just, to live her own life in spite of them.
But if the violence that’s been done to Adler’s character is bad, that’s nothing to what this kind of reading does to Holmes himself…
Sci-Ence! Justice Leak! 
Again, I am so relieved to see an intelligent commentary in Holmes. I never expressed it quite so well, but I was very upset by the BBC Sherlock’s warping of Irene Adler – and puzzled by the fact that Doyle,as you say a Victorian man against the female vote, is nevertheless more feminist than modern TV writers.
I cannot write ling on this yet (my phone is appalling) but just to say -yes.
It’s often the way with detective stories that the detective is peripheral to the story but central to the plot. Most of the story has already happened before the detective gets involved, and the events are driven mainly by the villains and victims, but it’s emplotted from the detective’s point of view. Doyle’s Holmes fiction is a fairly extreme example as Holmes often does surprisingly little investigating. The story might have a lot going on, but as you say, the plot mostly consists of someone going to Baker Street and telling Holmes and Watson a lot of things that have happened, and there can also be a denouement where someone else tells them even more stuff. (So incidentally, the success of Holmes is a bit of a problem for “show don’t tell” dogma.)
Good point about Doyle and feminism. Until I read this post I wasn’t sure whether it was intentional, but I had noticed that Holmes stories often emphasise how the law relating to marriage and property made women unnecessarily vulnerable, and imply that the abolition of coverture hadn’t gone far enough. Holmes usually believes vulnerable young women who come to him with unusual stories that the police wouldn’t be interested in, and he is usually concerned that these women are in danger. It’s unfortunate that Doyle often relied on the Damsel in Distress trope, even if he was using it to criticise society, but this does at least destroy any suggestion that Doyle’s Holmes is a sociopath.