It's hard to review a book like this, especially when you're not an expert. It's a bird guide. It's about parrots. If you've ever seen a parrot of any kind, ranging from the smallest parrotlet to the giant Hyacinth Macaw, it's in here.
I love the pictures, and I frequently look at this book if I'm depressed. Parrots always look happy. I know that's just the way their beaks and faces are built, but there it is. Like dolphins, they have a built-in smile.
Unlike most bird books, it's organized by region. That's useful--maybe even essential. At the macro scale, parrot territories don't overlap. You won't find a New World parrot in Africa or Australia, or vice versa (unless it's an escaped pet).
My one complaint is that this book says way too often that such-and-such a bird is "unmistakable." That's birder for "this bird looks so different from anything else, you're an idiot if you can't figure it out." And, yeah, if you're in Costa Rica and see a big bird (roughly 3 feet long) with lots of red (and blue, and green, and yellow), it's sorta probably a Scarlet Macaw. But have some more respect for the readers, please. Lots of things aren't "unmistakable" until you've seen them a few dozen times.
Parrots are extraordinarily intelligent, and a distressing number of species are endangered. They tend to live in areas that are subject to deforestation; they're also frequently the victims of unethical animal traders. Parrots of the World shows you what we're losing.
As far as the edition: Goodreads shows several books with the same titles, but different publishers and dates, by the same author. I don't know to what extent they differ. (I believe several of them are completely different books happen to have the same titles and authors.) While I'm usually cavalier about editions, my review is of the 2010 Princeton University Press print edition, although Goodreads only lists an ebook.