In the book Max is simply acting out a bit too much. Acting like kids do. He gets sent to his room for a time out and has an adventure, supposedly in his mind. At the end of the day, after having been more outwardly calm he “comes back” in time to find dinner waiting in his room.
In the film Max is frustrated because he perceives he is not getting desired attention from his older sister and his mother who apparently is dating. He acts out violently against both of them. After being chastised he runs away from home and travels to where he meets the Wild Things. He becomes friends with one of the monsters who has feelings similar to Max's. Through participating in various adventures with the Wild Things, Max comes to recognise his own bad behavior by seeing it happen in his friend. He travels back home to his mom and apologizes.
Both are good stories, but the movie has a great deal more depth and substance than the book did. The book serves as only a very skeletal framework for the movie's story. Outside of the distant implications of the broken home, I have trouble understanding how this film could be identified specifically as right or left.
But I have no problem hearing from anyone who has seen the film and wants to support a contrary opinion.