The book starts with the birth of the Cookie Monster. However gives no information regarding it's parents. I feel like that's an important information which is missing. The story progressed nicely after that walking us through it's childhood shenanigans. And finally introduced us the Monster in his teen years where he is shown as a frustrated adolescent who is irritated that people around him don't understand him and what he says.
In the end it is all happy as his babysitter understand him.