My five-year-old son thoroughly enjoys this book -- not for the mazes, but for the information it provides. And the title is a bit of a misnomer -- the book also features pages on prehistoric animals such as sabre-tooth tigers and wooly mammoths. One negative: the book is often difficult to open and flatten because of its original packaging in a plastic decanter shaped like a bone. My son's already crying about pages falling out. Also, one editorial nit (from my son): Deinonychus was 7 feet tall, not 7 inches.
My six year old is addicted to mazes, and these gave him enough to chew on. He ploughed through the book in a day and a half and would not be distracted. He did look at the answers for help, but it is still an accomplishment to finish the mazes even looking at the answers for assistance.
He wants to get another copy of the book and do it all over again.
The only other maze book I've liked this much for him is the fantastic "everything mazes".