In all the years I taught preschool and Kindergarten children that was certainly the best loved book of the hundreds I read to the kids. One little girl was frightened by the monsters in the book, but she was the only one who didn't love the book and ask to hear it read over and over again.
Probably every child on this planet with a normal family has experienced being punished for misbehaving, having scary dreams, and being reassured of their parent's love. No wonder so many kids can identify with Max.
Expanding a picture book into a full length movie certainly required adding a lot of material not included in the original story and I hope Hollywood did a good job of staying true to the original.