I believe Sherlock Holmes is now out of copyright, except for some very late stories, and I presume that's why there's been a surge of Holmes stories and the movie
I haven't read The Italian Secretary, so I don't know about it, but as a general rule IMHO the emulations fail to capture the combination of style, atmosphere, and character.
My view is, the moment you write in your own interpretation of Holmes and Watson, you may as well be writing your own detectives rather than using someone else's. For that reason I think if you're going to do it, you have to aim for ultra-emulation.
The only exception I've read to prove that view wrong is a book called Sherlock Holmes and the 1902 Fifth Test, by Stanley Shaw. In that book the narrator is not Watson, but another man entirely who's a cricket fan, and the POV character reveals Watson to be considerably smarter than the self-deprecatory biographer gives himself credit for. At the end of the book, the POV character and Dr Watson find themselves batting for England to save the test match, disguised as the actual players who were supposed to be there!
There was an SF anthology called Sherlock Holmes In Orbit which I read years ago (they took pains to say they had permission of the estate), and I thought a few of those stories were pretty good. They succeeded by not even trying to emulate the original style, and were so far outside the Canon that it didn't matter.
Another thing which the Holmes copyists do that doesn't work, IMHO, is mash him up with famous characters. (I don't know of a story in which Holmes meets Spock, but I'll bet someone's done one.) Or they introduce Holmes into famous incidents where he patently was not.
This sort of mash up is sensationalism for the sake of grabbing reader attention. But the essence of Holmes is that he eschews the sensationalist cases and applies his skills only to those which present features of interest, no matter how humble the client. (Okay, Conan Doyle himself broke that rule a few times, but that only proves even the best writers can get lazy, and those cases were rarely Holmes' best.)
The League of Extraordinary Gentlemen wisely excluded Holmes because his character would have been overwhelming.
If I were insane enough to try a Holmes story myself (and I might be that mad) I would stick to a short story, because that's the natural length for Sherlock Holmes. I would pick a humble client with an odd tale to relate; a case that presents features of interest, and I would target the earlier period during which Watson and Holmes shared rooms. In other words a classic Holmes tale. Then I'd allocate about a month to edit the short story into the right style, which would be very, very hard. Oh, and I'd include this line:
"You interest me strangely," said Holmes, leaning back in his chair. "Pray continue."