I recently received a review copy from Princeton University Press of Parrots of the World by Joseph Forshaw (amazon), which as the name implies covers all 350+ species of parrots in the world. This is a condensation of his early guide, Parrots of the World: An Identification Guide, designed as a typical field guide with an illustration plate on the right and brief text descriptions and range maps on the left. This redesign ends up being about the dimensions of the big Sibley guide but 2/3 of the length, so it is fairly suitable as a field guide, as it is marketed. However, I see little niche for world-spanning family guides as an actual in-the-field tool in my future birding - it would only be relevant for at most a couple dozen species out of hundreds on a trip to the neotropics, for example. However, I think this makes its niche as a light, cheap reference guide to the parrots, relative to its bigger and costlier parent book (although I have not seen this book in person to compare or to know how much information has been lost), so that is the angle I approach this review from.
Overall, I think the book is gorgeous, and succeeds thoroughly as a reference to the Psittaciformes. The illustrations are generally excellent and lifelike, although a few are depicted not in life poses but instead front/back views of museum specimens, presumably for subspecies for which little material is available to study. Illustrations average around 3 species per plate, so with the dimensions of the book each bird is fairly large. Some plates feel a little empty with too few spaced out illustrations, and I think a few more similar species on plates together is generally better for comparison, but in most places the book succeeds in balancing the number of illustrations per plate with illustration size. Similarly, the range maps are well sized, with my only major complaint is the complete lack of country boundaries on continents. This is balanced by brief notations in the text about range and localities to see the species, but boundaries would have been a simple, beneficial addition.
One major highlight of this book for me is the treatment of subspecies. Ranges of all subspecies are depicted on the maps and all are briefly described in the text, and many subspecies receive their own illustrations. In a few extreme cases this leads to a species like Rainbow Lorikeet taking up three plates itself, but I don't see this as bad at all. The comprehensive inclusion of subspecies is so critical for capturing the true range of variation in a bird family, and is also extremely helpful for understanding potential future splits.
Overall accuracy is a major benchmark for a reference work, but unfortunately I am in little position to evaluate this for most of the species in the guide. I have however spent some time birding in the neotropics, and I've even spent multiple field seasons doing research on a wild population of Green-rumped Parrotlets (Forpus passerinus). So, to check accuracy of course the first thing I did was flip to this genus. The illustrations for F. passerinus were a little disappointing for me - the overall structure of these birds is very accurate but there are subtle details in the plumage they got wrong. The male F. p. passerinus is accurate except they tend to have a slightly grayer wash on the nape. The female though definitely does not show such a distinct green face mask like the male as illustrated and instead has a variable yellow wash in the front of the face.
A pair of Green-rumped Parrotlets - male on the upper post. You know they had to make it into this post somehow!
Another major plus for this guide is the inclusion of flight illustrations, both upper and lower surfaces, for the majority of species. This is such an excellent feature I do not really know why its inclusion was not 100% comprehensive. A large number of my neotropical parrot sightings consist of birds flying past - such as slow, raucous pairs of Amazona or noisy rapid flocks of parakeets - so when country field guides fail to depict flight shots well they put birders at a disadvantage to identifying parrots. Also to this end the guide includes a neat figure in the introduction identifying many parrot genera by silhouette via their distinctive shapes.
The flipside to this is that Parrots of the World gets these distinctive flight profiles wrong for major Neotropical genera. It depicts the stocky, broad-winged and short-tailed genera, chiefly Amazona, as having narrow, pointed wings approaching falcon-shaped in both the genera chart and in every individuals flight shots. This is just a major glaring error. Take a look at the wing shape depicted for these Pionites in this sample plate from Princeton Press - the same swept-back pointed wing is depicted for Amazona.
Now check out this or this flight shot of Amazona parrots from Flickr. I don't think this ultimately detracts greatly from the guide's usefulness as an overall parrot reference, but it could impair field identifications and is ultimately just really annoying for those familiar with these species in the field.
One final pet peeve - the frequent use of "unmistakable" as a descriptive term for many species. First, nothing is truly unmistakable. Second, some species listed as such really don't deserve it. For example, both Hyacinth and Lear's Macaws are listed as unmistakable, and they are unmistakable as a group apart from most other parrots but they are most definitely very similar to each other and easily mistakable. Use of this term is bland and meaningless in descriptions of bird identification.
Overall, this is an excellent reference for anyone interested in general parrot diversity. It has a few minor flaws in design and some flaws in accuracy for some species, but I am still extremely glad to have it as an addition to my library.