This is a very quick read, and has some lovely illustrations by Skottie Young. The story was interesting (like Big Fish, but with time travel) and I enjoyed it somewhat, but it's my least favorite of Gaiman's books for younger readers. It lacks the poignancy of Big Fish, or most of Gaiman's other works, for that matter. He's shooting for a younger audience than that of The Graveyard Book or even Coraline, but this book only amused me, whereas the other two blew me away.
I could see myself reading and rereading this book back when I was eight, perhaps nine, but then I would have put it behind me. Unlike most of Gaiman's other books, which hit on many levels and work for readers of all ages, Fortunately, the Milk didn't live up to my (admittedly very high--it's Neil Gaiman, after all) expectations. Buy it for your kids, your nieces and nephews, but don't expect too much out of it for yourself.
Fortunately, the Milk, by Neil Gaiman, illustrated by Skottie Young