Most Sherlock Holmes stories (especially the short stories like The Red Headed League) are like playing chess in a Victorian drawing room. You get a period piece with some subtle moves. The Hound of the Baskervilles is a total change-up from that format. Doyle builds the atmosphere of ancient legends, foul play, and a dark moor in an irresistible way. You will find yourself looking out over your shoulder if you read this book on a dark, lonely night. So if you like a novel with a true gothic feel, this will be your main reward.
Your unexpected reward will be one of the most famous clues in all of detective fiction. In searching out who is haunting the Baskerville's, Doyle has Holmes solve the puzzle by looking for something that no one else was looking for. This is the only mystery that I know of that is solved by vacuous fulfillment (an odd concept of mathematics that Doyle must have known about).
The third feature of this story is the many fallacious beliefs about how science works (like phrenology -- the shape of the skull determining your mind and character). You may find this interesting or annoying. In either case, try to remember that we probably have many similar false beliefs today that will look silly a hundred years from now. Can you think of one?
Wrap up in a blanket by the fire, have a glass of wine, and shiver with anticipation!