"39 clues"

Has anyone else heard of the 39 clues series? What do you think of it? I have read the first one and wondered if it was worth it to read the rest or is it just a cheap trick to sell books.

My son (8) is really enjoying the series. He also plays some of the online games associated with it. From the ones I read, you can tell the books are written by different authors, but it's a fun adventure and lots of interesting history and geography in as well.

they are checking out a lot in my school....seldom make it from the book truck to the shelf...the kids don't seem to care if they are reading them in order, either. Just got the whole set last month

thanks. I will have to try to find more of them though maybe I will wait until the contest is over so not so many are out at the library