The book tells the story of how Sherlock Holmes and Dr. Watson came to be partners and details their first murder case. Like every other conscious person in the western world, I have always been aware of Holmes' titanic status in our popular culture, but this is actually the first story about him that I've ever read. It's very entertaining to follow as A. Conan Doyle introduces the various facets of the Holmes legend: we meet Gregson and Lestrade, watch Holmes and Watson take up lodgings at 221B Baker Street, and are introduced to Holmes' violin playing, pipe smoking, snuff addiction, and, of course, his incredible powers of deduction, which are a marvel to all that surround him. Watson's musings on Holmes' nature are often quite humorous as he attempts to figure out this eccentric individual.
The mystery itself is quite good. Many have remarked on how the story derails with its lengthy digression to the back-story of the murder, which occurred in Utah. This part of the story is sure to offend Mormons, who are here portrayed as a cultish fascist state that will resort to officially sanctioned murder to accomplish its ends. Doyle appears to have been reflecting the prejudice of his time, and this is a very unfortunate and disappointing aspect of the novel. However, if you can look past that, perhaps by imagining that they are some fictional cult, this section of the book is quite effective and suspenseful in its own way. However, the major strength of the story is, of course, Holmes himself. I think that Doyle quickly realized this and focused on Holmes much more closely in later stories.