At first I was a little worried: some of the writing in the opening chapters is a bit clunky ("Alex's bushy light brown hair squatted on his head like a chicken laying an egg"), and Moore's main character in the modern plot, scholar Harold White, is one of those characters who is at once intelligent and also stupendously stupid. The plot as it unfolds is somewhat improbable (and the ending even more so), and just about all the modern characters were quite unlikeable.
The Conan Doyle storyline was much more entertaining, sort of in the vein of Julian Barnes' Arthur & George, although once again there were a few elements (including a very unlikely episode of transvestism) that strained credulity.
Overall, if you're a fan of Holmes pastiches this is another to add to your shelf, and it does make a fast, entertaining read (great for a plane ride, I found), even with the eye-rolling moments. In all likelihood I'll read whatever Mr. Moore comes out with next; I think he's certainly a writer to keep an eye on.