Like the other reviewers here I too bought this for a little one (12). So I will try not to repeat what they have already mentioned.
Having had one or two of these as child I was shocked and delighted when I came across them. First things first these books are fantastic for getting children to read more. And by playing along with them you can spend some quality time together and help imrpove their vocabulary at the same time. Some of the books also have some side puzzles that can be solved on the internet which adds an extra dimension that to be honest I probably enjoyed more than they did. For example you might get a link to a site that shows a picture of the haunted house you are in, that picture then reveals clues, which can help guide you down the correct path. These are not essential to do but again do add an extra dimension to the book and at the risk of sounding repetitive are also a fantastic way of getting younger kids or the whole family involved.
I highly recommend these books. Enjoy