I picked up this field guide after about a year of really being into birding. I was advised by many other birders to have at least one other field guide to compare and contrast when trying make a tricky identification. The Sibley Field Guide to Birds of Western North America has been my go-to field guide for the last five years, but because I tend to lose my field guides so frequently out in the field, the Nat-Geo field guide has steadily served as a solid back-up.
The cover picture shown above is of the 5th edition. I actually have had a copy of the 4th edition. I have seen that the 5th edition sports thumb tabs, which is a nice touch. There may be other changes to the 5th edition that may make some of my comments below irrelevant. Please bear with me as I free-form ramble about my thoughts of the advantages and disadvantages of the Nat-Geo Field Guide.
The cover of this guide is a glossy card stock with a plastic coating intended to help it weather the weather. It has for the most part, but the plastic is starting to separate a bit. Other field guides come with a more vinyl-type covering that seems a little more durable.
I like the thumbnail-sized range maps for each of the species next to its entry. The maps do show state/province boundaries which I prefer. The species are listed in taxonomic order which is pretty much standard anymore. Some field guides list birds by similar shape, size, or color, which may work for some, but drives me nuts.
The artistic renderings of the birds is quite good. In my early days of birding, I thought it was too busy for my eye, too much detail, especially compared to Sibley. Sibley's guidebooks when compared side-by-side are very focused on highlighting the differentiating features. Sibley intentionally leaves the non-essential parts of the birds somewhat washed out in his paintings. With a little more birding experience under my belt, the detailed artistic renderings in Nat-Geo are actually quite impressive.
The descriptive paragraph is pretty standard, giving information about the physical appearance of males, females, and juveniles. It includes song/call onomatopoeia and a mention of range and frequency. I still prefer the Sibley layout overall with the horizontal line separating the species as it lends to a more simple and intuitive feel. The plates with multiple species paintings laid out on them often felt too busy for me. To its credit, Nat-Geo does appear to show a few more plumage variations than does Sibley's.
I like Nat-Geo's "Quick-find" Index in the back. I just wish it was the very last page rather than being found just before the artists' credits. Sibley's Quick Index is in very back and made of card-stock paper. Because it is a different paper type it is really easy to find quickly, as it should be. The regular index in Nat-Geo is user-friendly enough and also includes check boxes for you to mark which species you have seen. This must be a throw-back to the days before eBird where the average birder kept his life list in his field guide. It almost seems unnecessary in my world now, but I am certain there are lots of birders out there that still like this feature.
Price: as low as $9 + shipping online
So my overall recommendation on the National Geographic's Field Guide to the Birds of North America is that every birding should have a copy of it...at least as a back-up.