It has been a couple of years since I read this, so this will not be as thorough as I would like. I read this book because it fit a category on a required reading list and because of it's title. I love anything (ok, almost anything) Sherlock Holmes and of course recognized the famous quote at once. I did not expect to like this book and found myself very pleasantly surprised. The unique set up and unfolding of the novel is wonderfully executed and really helps the reader get into the mind of this unique young man. Though the boy's condition is never named, most believe he has Asperger's Syndrome; I rather like that you are never sure. I was surprised to discover he had not done any research on the syndrome before writing this. His descriptions are accurate and I was reminded of a couple of children I met while substituting. This really helped me understand how they might view the world. The mystery is admittedly not very mysterious, but that is not really the focus of the book. The main character is and his development during the plot is handled very well. It is difficult to describe this book unless you have read it. It is not set up as a normal novel and that is not a bad thing. It would loss a great deal of its effectiveness if it had been written in any other way.
The set up of the book might bother some readers. I can see where that might happen, though I was not. It is also a book it is best to go into with few expectations, because in my experience, it doesn't meet them. That is not to say it does that negatively, but it is a difficult book to have expectation of. This is a book you have to take or leave and that will be different for each individual.
A book well worth giving a try, but one to go in with the knowledge that it will surprise you (for good or ill).