Have you ever read the original fairy tales? Some of them are down right scary. Adam points out in the beginning of his books that these are not the kid-friendly versions, but they are also not as adult as the originals. There may be some dismemberment but characters stay clothed.
More than a retelling of fairy tales, Adam Gidwitz is like the MST3000 of fairy tale narrators. Adam points out the life lessons in the fairy tales that you might over look, along with the "foolish" decisions of some of the characters, His wit and humor are well used in pointing out why on earth a frog would fall in love with a beautiful cruel girl just because she is beautiful.
The review copies I was provided with are just a tad long than the "nook samples" you can download from Barnes and Noble. (one full chapter in the first, and a section surrounded by blank pages in the companion.)
So I can not tell you that I enjoyed the whole book or even know where Hansel in Gretel come in. But what I did read was delightful. I would be interested in reading both books in their entirety.