My niece liked this book and identified with the idea being presented here. I'm sure she would have given this book three stars, which is why I gave it three stars.
That said, I thought Lily was an unpleasant child, whether she was having trouble adjusting to her brother or no. Lily's nastiness and snottiness persisted from beginning to end, and that just got to be a bit much for me. I would probably give this book one-and-a-half stars, but it's been a long time since I've had to adjust to a new sibling, so I'm probably forgetting what that was like and as a reult, missing something here. My niece took this story in stride and definitly did a better job than me of understanding that Lily's behavior was written big for the sake of impact and/or comic effect. She liked it, I didn't, the book was written for kids, so her stars win over mine.