The repetition of the story makes it easy to read and easy for an older child to learn, and yet isn't the kind of repetition that drives parents wild. As the child gets older, you can drop words and let them "fill in the blank" as they look at the pictures to identify both the animals and the animals' colors.
When I was a Nanny my charge and I adored this book and read it at least a hundred times. Now that I am home with my own son, I bought the book for him and he loves it too!