It's the most comprehensive general field guide available. It covers more of the rarities than any of the rest, including species found in such places as the western Aleutians of Alaska and the Dry Tortugas of Florida. The book depicts and desribes 80 species that weren't in the previous edition. This is a beautiful book. The illustrations, contributed by many artists, are excellent.
Concise text draws attention to significant field marks.
Range maps show where the birds can be found in summer and winter. Some of the maps are so small as to be difficult to read, but they are well located, on the page facing the pictures and next to the text about each bird. Although the book is a bit larger and heavier than other field guides, it is worth the extra effort to have it along. Even if you prefer to carry a smaller book in the field, you'll be glad to have the National Geographic Guide to consult when you get back to your car. Some beginning birders may be overwhelmed with the great amount of information available in this field guide.