Brilliant! Dahl tells the story of a British boy whose parents die, and he lives with his Norwegian grandmother. She used to hunt witches and warns her grandson that witches are still around and are very dangerous; they aim to wipe out children completely. There's even a Grand High Witch who oversees all the witch activity throughout the world.
I have to say, the movie adaptation is really good. We used to watch it all the time when I was growing up. And honestly, I don't have any complaints with the book. Read it!