I'm used to reading books written before 1900 or shortly after, and I'm accustomed to Conan Doyle. Even so, this book is so ridiculous, as if it were written by a Frenchman, not by a Briton. It really is as if it mocks the French writing style of the times before the Second Empire, with dialogues nobody would carry on this way, and with uselessly long descriptions. Typically French, only this time it's an English text. If you read it as a pubescent, maybe you'll find some charm in it, otherwise it's a joke of a novel.
If you want naive writings of much better quality, you could pick your crop from any of Balzac, Dumas, Zevaco, and a lot more, except that they didn't write stories around Napoleon (Dumas and Walter Scott wrote about Napoleon, but their attempt was at a biography of the Emperor).
If you want to read non-Sherlock works by Conan Doyle, there's plenty to choose from. This one is only too subpar.