This was a slog. And I mean that in the best possible way.
As I pointed out waaaay back at the beginning of my current read-a-bunch-of-guidebook endeavor, field guides are not meant to be read cover-to-cover. But even if I'm simply going to haul a field guide out with me for, say, birding, I'm going to have to have perused it as much in full as possible, beforehand, so that I have a sense of how to locate what I'm looking at. It's easier for me with snakes and frogs than with birds, not only because I'm generally far more familiar with these things, but also because there are so many fewer species to try to recognize. So taking on a project of this scope is, for me, a major exercise in horizon-broadening.
So the "slog" is in visiting every page, reading every description, checking out the distinguishing factors that divide up subspecies or denote closely-related species, and then in cross-referencing those descriptions with the color plates, which I suppose for publishing reasons are all kept together, quite separate from the sections referencing them. Some of the photos are of little use in helping you identify what you're looking at, because they are so blurry or distant, but I suppose there's only so much time the authors can spend on collecting high-quality material before they have to go to press.
The "in a good way" applies because although at times it was tedious, I never felt compelled to put the book down and give up. It took me longer to get through than I hoped, but there was a certain sense of accomplishment in the end.
If you're a dedicated birder, of course, then you won't have the same considerations, and will undoubtedly find this an indispensable field reference.