I don't think I'd name any author as 'can't be touched', but Dahl is a tough act to follow. Rowling is not Dahl, not in voice or wild creativity, but she hit some kind of a nerve in kids with her book. She does find more of her own voice later on, I think, but I would characterize the tone of all the books as "British" in a way I cannot explain well, but have also seen in such as Diana Wynne Jones.

I think it has to do with it being a simple story about a popular jock boy with a special magical destiny who is opposing both genuine evil and incompetent adult authority. The magic is simple and fairly magical-seeming--though they are learning it for school, it's still magic. Who wouldn't rather do that than Algebra?

Don't look for depth, in other words, but it's not terrible. It's just fluff.