I'm going to come right out and say this. I love Sandra Boynton. To me, she is the most prolific children's story writers to come out in this generation, specifically for younger children. I put her alongside Dr. Seuss and Robert Munsch, and that's high praise.
"Moo, Baa, La, La, La" is produced by Loud Crow, the makers of the PopOut! book series (Peter Rabbit, Night Before Christmas, etc). Their books have been showcased by Apple for a reason, they are top notch in quality and production values. Designed to simulate a real "pop-up" type book, they include characters that spring when you touch them, tabs that move various parts of the book, and windows, doors and such that open and close. It really does give the books a tactile feel, and I honestly believe these books have more interactive elements than most on the app store.
It's clear that "Moo, Baa" is a silly book. It starts out normal, with a cow saying "Moo", a sheep saying "Baa", but the next page you lift up a curtain and it's 3 singing pigs saying "La, La, La!".
Like with most books in the app store, you can choose to read it yourself or have "The Big Guy Read it" for you. This book has an especially special narrator, Sandra Boynton's son, Keith (trivia fact, Sandra's middle name is Keith).
Inside, interaction ranges from touching Rinos to hear them Snort and Snuff, pulling back dogs like a slingshot to send them running at 2 cats saying "Meow". As the dogs leap after them, they leave their collars behind to hang in mid-air, a very cute touch.
Like most "board books", it's short, coming it at about 12 pages, but it's no slouch. Each page offers so much to the touch, almost everything you see does something, even if it's as little as a sound. My daughters spent probably twice as long enjoying the pages, the interaction, the art and the humorous sounds as they did of just the story. Hearing them laugh while touching each of the singing pigs at the start never gets old.
Now, the story itself is probably targeted to younger children around the age of 1 - 4, because of its simple language. The sentences are simple and they mostly consist of animal sounds except for the last of the book. It's a magical ending and one that will yield different results for everyone who reads it.
I would like to make it clear that even though the book is designed for younger children, you don't have to be young to enjoy it. My daughters are 6 and it is still one of their favorites. Because they're now fairly advanced readers, they're able to read the entire story easily and without having to struggle. In the path to learn how to read, I find this is far more important than pushing kids to read longer words before they're ready. I figure they'll probably be done with the book in a year, but between the physical book and this, I've gotten an easy 5 years out of it, not a lot of books that have that kind of staying power.
So, is "Moo, Baa, La, La, La" worth your $3? Yes, yes and yes. It's a simple story that's an amazing read for children, especially ones who are very young. It scales to older children who are learning how to read, and allows for easy comprehension. The app design is great, and the interaction is one of the best on the app store. You owe it to yourself, and your kids, to check it out.