The Penguin Guide is a well-written, informative survey of the field. It's the only jazz review omnibus I return to for pleasure, rather than for reference.
While this tome is more opinionated than competing reviews, it's good to have a consistent frame of reference. You learn what the authors like and dislike, and can apply that to your own preferences. The essays that accompany the ratings avoid the redundancies found in the All Music Guide, and do a better job of placing the recording in the context of an artist's career.
Because the authors are English, however, much of the discographical data isn't very useful for American consumers. Also, the representation of American labels can be understated. For example, there's a lot more Blue Note CDs in print in the U.S. than in Europe, leaving some notable gaps in an artist's output. Fans of other American labels and artists might find similar holes in the discography.
The flip side of its European focus is that you get reviews of artists and releases usually ignored by American reviewers. And the English/European jazz canon is different than the American version, making the Penguin Guide something more than the Revised Standard Version of the received wisdom you'd find in an American omnibus.
I wish the Penguin Guide would follow the example of the All Music Guide and simply review the important albums, deleted or not. Eventually those Bobby Hutcherson titles (to choose some personal favorites) will return to print, and when they do, you won't be able to consult the Penguin Guide, unless you wait for the biannual update.