This guide is a combination of the previously separate Eastern and Western Peterson guides. The look and feel of this guide will be immediately familiar to any users of past editions, especially the latest Eastern. However, every aspect of the book, even the art, has been enhanced and updated. Here is a brief summary of the changes.
The book's size is the first change that will be noticed. It is now probably too large to carry into the field. However, the increased size means that the plates are less crowded, and the art can be reproduced in a larger size. This allows the art to be better appreciated and studied.
Unless you are extremely familiar with Peterson's art, you won't notice many changes on the plates. But there have in fact been many. The most extensive changes have been in the form of digital enhancements to Peterson's art. These are touch-ups and corrections to make the bird on the page look more like the bird in the field. Thankfully, these enhancements have been artfully done, and do not stand out. In virtually every case they have indeed improved the image of every species that I'm familiar with.
There are also entirely new paintings, contributed by Michael O'Brien. Some, like the Himalayan Snowcock, are new species that have never before been included in a Peterson guide. But some previously included birds have been completely replaced by new paintings. These have been done in Peterson's style and some are very difficult to pick out. However, many are fairly obvious. They are not bad by any means, just different, and that difference can be jarring.
Like the art, the text has also been extensively enhanced and updated. For the most part, this consists of editorial changes such as word usage. But there are some significant changes, such as new field marks.
Likewise, the maps are entirely new. They are done in the same format as the previous Eastern edition, but the data they are based on is up-to-date, and supplied by the foremost expert in North American bird distribution. There is an entire section of large range maps in the back of the guide, and each species account includes a small thumbnail map. The thumbnails are much larger, and infinitely more usable, than those included in the Eastern regional guide.
As with the previous reviewer, I feel that although this is a good field guide, it does not reach the mark set by other recent guides. However, I still recommend it because Peterson's art has never looked better in a field guide. The art here looks a little better than in the latest Eastern edition, due to the increased size. Compared to the Western guide, however, it is a revelation. The same paintings in the Western guide are dull and soft. But here they are vibrant, and you can see more of the fine detail.
As a reference, this guide is superior to the previous Peterson regional guides, yet not quite as good as some other North American guides. But for me, the showcasing of Peterson's art makes up for this, and makes it well worth having.