The lost children. The gingerbread cottage. The scary witch who, however, doesn't see very well and can easily be fooled. All elements of one of the darker Grimm fairytales. All here in this retelling, along with the explanation of where the children's names come from. (When you think about it, if this had been a British folktale, it would have been called "Johnny and Maggie" or Meg or even Peggy, none of which have quite the same ring to them)
If you're going to have a folktale retold, especially such a dark one, Neil Gaiman is a good one to do it. The average retelling is just that - a straight retelling which isn't by the Brothers Grimm or whoever. "Once upon a time..." And then the writer and publisher decide just how much of the original story can be told, depending on who is having the story read to them. For example, you really don't want to describe Cinderella's stepsisters cutting off toes to fit into the glass slippers, do you? Not at bedtime, anyway.
One thing about folktales is that you never learn reasons, such as why parents would throw their children out of the house to die, even in a famine. Neil Gaiman suggests war and thieving soldiers passing through and taking away all the food sources and destroying the fields. This version even suggests that it may be a reason behind the witch's cannibalism, though not entirely; from the description of what Hansel and Gretel find hidden around the gingerbread house afterwards, she sounds more like a serial killer than a poor old pensioner who is as much a victim as anyone else.
At the end of the book, the author talks about the possible origins of the story in the time of the Plague, when all sorts of terrible things would have happened and family relationships broke down.
The book is basically an extended retelling rather than a twist on the original tale. If you're expecting something along the lines of The Sleeper And The Spindle, you may be disappointed. But as a retelling, it has class, and the beautiful moody black and white art of Lorenzo Mattotti supports it well.
If you're going to buy a version of this folktale to read to your children, this one is the way to go.
I hear there's a movie of this book planned, or at least optioned. That should be most interesting...