3 stars
There was nothing necessarily wrong with this book. It was entertaining and funny to the degree I expected of a George Beard and Harold Hutchins original.
However, I think Dav Pilkey kind of wrote himself into a box with the Captain Underpants/Super Diaper Baby series. The book greatly lacked the gross-out humor of the other books. It was still good, but I missed that raw disgust I felt when Super Diaper Baby literally fought a piece of poo or when Captain Underpants got eaten by a giant toilet. There was a little, tiny glimmer of gross stuff in this book, but it pretty much just stopped at purely-liquid puking (that really just looked like water). This may sound weird, but as a grown-up, I wanted this book to be grosser.
Having said that, I still liked the story. It was still ridiculous like the others with a weird, all over the place plot. But I would say this one relies more of awesome-ness elements (cavemen, dinosaurs, kung-fu, time travel) than gross-out humor.