I know this is trite to say, but the BOOK WAS SO MUCH BETTER.
If you're wondering, they excised about 2/3rds of the book for the film. The novel is written in alternating chapters from a first person perspective from Oskar and letters written by the grandpa to the dad and the kid. The book is about all three Schells, the movie is just a tear jerker about the kid. I didn't think the film was that bad, really, but it wasn't an accurate depiction of the book. The novel is one of my favorites OF ALL TIME EVER.
And now the book is ruined for you by watching the movie. Ugh.