I was fairly intrigued by this book. I very much enjoyed Pete Dunne's Hawks in Flight, a book written in chapter style that relies as much on the description to create an image of the bird as it does the illustrations, probably more so than any identification book I've encountered. In this day and age of SLR photos however, it's unlikely many bird books will ever be as successful as that one with it's huge ratio of words to pics.
This book tries to encompass some of the description, while still showing pics of most ages of most of the species. Dunne italicizes a lot of the pearls and key points in many of the paragraphs and I think that brings out his style when he does. When he isn't italicizing it feels like it bogs down somewhat and becomes more general.
Here's a sample page...
The photographs that are chosen are excellent, but sometimes feel a little random which I think is because they're essentially all Karlson's photos. For example, in the Sabine's Gull chapter they spend a couple paragraphs discussing one of Karlson's photos that was also in Howell and Dunn's gull book with regards to aging. I don't see any way this discussion takes place if Karlson isn't overwhelmingly accounting for the photos.
If you're looking to finally take the plunge and learn the gulls, it's a lot more readable than either the Howell and Jon Dunn book or the even more ponderous Olson and Larsson. If you already have 2 or 3 gull specialty guides on your shelf, I'm not as sure this is going to add as much.
One significant drawback in my mind is that the authors spend very little time on potential rarities. I recognize that the chance that any of us is going to find a Slaty-backed Gull isn't particularly high, but I would have given that species an equal amount of content as the common North American ones since a lot of more advanced birders are going to be looking for them.
There is a quiz section in the back of the book which is fairly entertaining. I don't like that they don't give the location of the quiz photos however. Withholding that piece of info feels at odds with their goal of focusing on the regularly occurring species.
Overall this is a well-done book and I think a lot of people who want to tackle learning the gulls will find it exceedingly helpful.