I was scanning the library shelves when I happened upon the series. Now, I have never been a huge mystery fan, but a good mystery book is always an enjoyable read because you are making your assumptions/predictions as you read. I hate a book that is completely predictable. Sammy Keyes is not predictable in the least. I actually found myself making a prediction, only for it to be thwarted a chapter later. I would assume that that is exactly what Van Draanen wants the reader to experience. One minute you think you have the mystery solved, but the next minute you are changing your tune.
All in all, this is a great series. It is cleanly written (which I am a HUGE fan of), but it has characters that the reader can easily relate to and want to relate to. Sammy Keyes is a girl, so most of your boys will not like this book, that is adventurous, a bit tomboyish, and loves to solve cases. She seems to not be afraid of having a little action and adventure in her life. This book/series is great for grades 4-7. If you have a strong reader you can give them the book in 3rd grade because it is cleanly written and they will still be able to relate to the story. Now, if you have a girl between 4th and 7th grade then try giving them this book; they will love the book and ask for another in the series.
There are many series books out there. Children and adults seem to like series books because you already know and love the characters. Therefore, if you are looking for a new series to read because your child has far outgrown The Magic Treehouse books, then give her a Sammy Keyes book. Oh, and one last bit of information for you. This is a series that you do not have to read in any order. You can jump around among the various books and love them all.
Enjoy! I'd love to hear you or your child's thoughts of any of the Sammy Keyes' books.