I never encountered Mrs Piggle-Wiggle as a child, but I know that many people who did really adore this series. Coming to it as an adult, I feel like I've missed out on some kind of special magic that it must have, because while I liked it well enough, it's hard for me to see how it could inspire such fond devotion.
I read Mrs. Piggle-Wiggle to my six-year-old, having just recently resolved to make more of an effort to read aloud chapter books to him (we've been stuck in a loop, reading the same picture books over and over), and he was really enthusiastic about it, so perhaps when he's an adult Mrs. Piggle-Wiggle will have that magical glow of nostalgia the Winnie-the-Pooh has for me.
I quite liked the first chapter, in which we meet Mrs. Piggle-Wiggle and see her upside-down house, and watch her interacting with kids and showing them how washing the dishes can be a tremendously exciting game. So it was odd and disappointing that for the rest of the book she doesn't appear at all except as a disembodied voice on the telephone. Each subsequent chapter is about a different problem child, and the mother's desperation, and Mrs. Piggle-Wiggle's wacky cure. I found it got quite repetitive, and though my son was relishing each child's bad behavior, and was eagerly anticipating what form the cure would take, he still got a little impatient with the part of each chapter in which the mother (they are all indistinguishable from each other) calls all the other mothers that she knows for their (completely inadequate) advice, until one of them will say "Why not try calling Mrs. Piggle-Wiggle", and the mother says, "Oh yes, what a good idea!". By the end of the book, we were both yelling, "Just call Mrs. Piggle-Wiggle *first*, already!".
But, as I said already, my son liked it, and that's really what matters. I'm a little uneasy though. This morning he said "The never-go-to-bedders cure was so funny! I think I'm not going to go to bed tonight so you can try it on me!"