My natural history interests are mainly in botany and mycology, but I also have an interest in birding, and I own dozens of bird identification books, and this is one of my favorites. Although there may be better books for the field or for home reference now, such as the newer Sibley, Kaufmann, or Smithsonian books, this is still a good work for general identification purposes, and it's served me well for that. Since this one was written there has even been a large, Reader's Digest volume about 10 years ago that was actually pretty well done, I thought, so everybody seems to be getting into the act.
As another reviewer here perceptively pointed out, the paintings in this book are more modeled and 3-dimensional looking, compared to the classic Peterson book, which look flatter and less solid. Also, the colors are more muted, and therefore more realistic to me. Both the Peterson and NG books have good field notes and tips on behavior which are useful. The 3-volume Smithsonian guides have great pictures, of course, but they're better for home use since carrying three books in the field usually isn't practical.
There are other specific differences between this and the Peterson book, but others have already pointed these out here, so I'll just conclude by saying if I had to have just one guide, this would definitely be in my top 3 for the honor.