What I loved: The book is quite clever in design, and the big appeal is definitely in the folding out to become the firetruck, complete with the flaps for the doors lining up to open and show the driver inside and a ladder on top that you can lift. The illustrations are great and lead to the cool toy-like element. The rhyming text adds a little fun if you want to also enjoy the book. In terms of the book content, there are some really cool pages that helps to show some firefighter skills, such as the pull tab that moves to show a firefighter putting out a small fire with her hose.
What left me wanting more: In terms of the book, it would have been helpful to have things labeled for items that parents might not know. It also would have been cool to have more facts about firefighting or how the tools, gear, and truck might be used (though there is a little bit in there, it would have been cool to have even more).
In terms of the buildable truck, it is a little confusing to make the first time, but it's definitely doable. The truck is not stable when moved, so it is not one that they can really play with but more of one to look at once built. The bending of the lift-the-flap dress-up firefighter also weakens the seam, and ours tore pretty quickly there, likely because the book is already a little weakened there by the double flaps.
Final verdict: An overall fun cross between toy and book, WHAT'S UP, FIRE TRUCK? is a clever design for firetruck enthusiasts. Recommend for toddlers and preschoolers.