I don't think one could quite call this a "complete" guide to prehistoric life, however it is very informative and a lot of fun to read. The many computer-generated graphics in the book are generally very good, they do a nice job of bringing the animals to life.
The book is divided into three parts, covering the four geological eras, the Precambrian and Paleozoic are both covered in part one. Each part opens with a high level overview of each of the periods of that era, I think these overviews really tied the book together nicely. Following this a selection of animals from that era are presented; with one exception, there are no animals from the Precambrian. Typically one or two pages are devoted to each animal, including text and graphics. The computer-generated graphics are ubiquitous; sometimes there are photos of fossils. I thought the text was very informative and interesting for every animal, not a bad section in the entire book.
I liked the selection of animals. Not surprisingly the animals covered were biased to those with extreme characteristics, e.g. the biggest arthropod or the largest land predator. There were the animals that show up in pretty much every book of this type, for example: Trilobites, Haikouichthys, Dunkleosteus, Stegosaurus, Tyrannosaurus, Smilodon and Megalodon. There were also some that seem to be less commonly covered, at least in my experience: Pterygotus (a nine foot arthropod), Arthropleura (an 8.5 foot arthropod), Lystrosaurus (an interesting looking therapsid), Leedsichthys (an 88 foot fish), Didelphodon (a cretaceous mammal), Doedicurus (a huge armadillo) and many more.
Based on page count, or number of animals, the presentation clearly leans towards the Mesozoic. Animals from it accounted for almost half the pages, while the Cenozoic accounted for about one-third and the Paleozoic accounted for about one-sixth. Some arthropods are considered in the Paleozoic, but after this it's mostly only vertebrates are covered. Plants aren't mentioned at all. Not a bad thing or even surprising, but given the title of the book I think it should be pointed out.
One the whole I thought this was a great book. For books of this type, the main part being a catalog of animals, it's my favorite.