Reddit mentions of Locked

I adore Loren D. Estleman's earliest Sherlock Holmes works, outre as they are, because even though they feature Holmes up against Dracula (Sherlock Holmes vs. Dracula: The Adventure of the Sanguinary Count) and Dr. Jekyll/Mr. Hyde (Dr. Jekyll and Mr. Holmes) the two novels are wholly at peace with the canon and written in a remarkable approximation of Doyle's style. Estleman's later efforts are not very good and best avoided.

Ten Years Beyond Baker Street is a remarkable book, and quite possibly the most enjoyable Holmes pastiche I've ever read. Holmes is grumpy, Holmes is retired, and worst of all for him, he's pulled out of his snug home on a icy winter's night to find a missing secret agent. Yes, this involves the infamous Dr. Fu Manchu, but that doesn't reduce the enjoyment of this wonderful novel a single bit. It's massively enjoyable. Take note that Watson only plays a minor role in the story. Instead, the story is told in a nearly perfect approximation of Sax Rohmer's style.

If you wish a novel that sticks much closer to the canon, I highly recommend The West End Horror. I didn't care for Meyer's first novel, which meandered and had a hugely disappointing climax. Nor could I ever make it through his third novel. But The West End Horror is monumentally fun, even with a unlikely, bizarre ending.

When it comes to newer authors, I enjoy Eva Morgan's Locked (even though it couldn't be less canonical if it tried), Nicholas Briggs (from the absolutely fantastic Big Finish audio drama series), and James Bojaciuk (responsible for "Imprisoned, Half-Dead: a Syllogism" and the kinda-sorta-vaguely-Holmesian "Cemetery Games" ).

I also greatly enjoyed A Night in the Lonesome October, All-Consuming Fire (though the last third is awful), and Kim Newman's magnificent novel Professor Moriarty: The Hound of the D'Urbervilles.