I love the message and meaning behind fairy tales, and of course kids love them because they are short and generally feature protagonists with whom they can identify. Unfortunately, the genre teaches very little about good writing, and as a result we teachers are often subjugated to students' stories which starts "Once upon a time..." regardless of genre.
Mike Klaassen's adaptations of fairy tales take the meat of the original source material and actually turn it into something fuller and more satisfying. The kernel is still there, but the point of view is expanded and becomes deeper, the details are more lush, and the tale, as a result, reads more like a well-structured short story.
Hansel and Gretel is told from a third person limited point of view, in Hansel's head. We experience in greater depth his fear and determination. I agree with the author that comparing this novella to the original Grimm text could help writing students get a better grasp on deepening point of view, exposition versus scene, and pacing.
The author does not shy away from the gruesomeness of the original story, so, parents and teachers, read it through before deciding whether it is appropriate for your children.
My one complaint would be the alterations in the story which marginalize Gretel. In the source material, it is she who pushes the witch into the oven. In Mr. Klaassen's version, Hansel does. In addition, at the end of the source material, Gretel calls a duck to help her and her brother cross a stream. That part is cut form Mr. Klaassen's version. Gretel is stripped of her strengths and is left relying entirely on her brother. Yes, the witch supposedly teaches her how to trap game, fish, and tend the homestead, but none of that happens on screen, so those contributions are largely meaningless. I do wonder what the author's motivation was in those changes.