Fortunately, the Milk is a tall tale told by a father who went out to get milk for breakfast and took an incredibly long time to get back, so he told his kids a fantastic story about time-travelling dinosaurs and pirates and wumpires and other funny things that kept him from getting back right away. The book is chock full of silly illustrations by Skottie Young, which I found almost as funny as the book.
Sam liked it pretty well too, though he only read it once, which means he didn't love it. I liked it enough to plan on seeking out more of Gaiman's books.
If This Was a Movie, I Would Rate It: PG for some mildly worrisome moments involving danger from volcanoes, wumpires, and pirates, etc.