jj21 is spot on with silly and unbelievable - but they're the main reasons why this book is such rattlingly good fun.
It's quite a departure from some of Neil Gaiman's other, more contemplative, children's books that are written for a similar age group, such as The Graveyard Book, Od and the Frost Giants and Coraline (all of which I've read and enjoyed). That is not a bad thing; Fortunately, The Milk is an absurd and witty old-fashioned adventure that careers along at breakneck speed. Neil Gaiman must have had fun writing it, although it may not have seemed like it was fully under his control sometimes!
The premise itself is clever, a Dad telling his children about the adventures he had buying milk, and I enjoyed watching for how many times the phrase "Fortunately, the milk" came up. The action storms along with many, yes, silly and unbelievable scrapes and rescues from danger without pausing for breath. In its 140 pages the story bounces from alien abduction to pirate mayhem, from human sacrifice and volcanoes to Houyhnhnm-style ponies and vampires, culminating in the sheer chaotic collision of aliens, space police, dinosaurs and dwarfs, straight out of a screwball farce. Not to mention an encounter with a memorable time-travelling hot-air-balloonist called Professor Steg.
Chris Riddell's lovely, witty illustrations add even more pizazz to the story and make it feel amost like a graphic novel, which should encourage more reluctant readers to pick up the book.
On an adult level, there we a few things in the story that I particularly appreciated. I identified with the Dad who was oblivious to everything around him when he had his head buried in his newspaper. I liked the children's observations and comments on the story as it unfolded. Mainly, though, I was delighted by the reminder that all the inspiration needed to tell a good story can be found simply by looking around you.
Children aged 8 + should love it!