As usual with the series, this book does a very good job at introducing the "essential" birdwatching sites of a huge region.
Much of it is, for better or worse, devoted to describing the two biggest and most visited countries, Australia and New Zealand. Coverage of these is good, but since there are also single country guides to them you could also use those.
Where this book really becomes invaluable is its coverage of the often little-known archipelagos of Oceania: Melanesia, Polynesia and Micronesia. Few of these countries are often visited by birders, yet even the remotest ones, like Pitcairn, are described. Since other guides to nature reserves of these island nations are basically non-existant, descriptions and maps of remote islands and forested regions are of interest to anyone with an interest in the fauna of the Pacific.
But of course, twitchers are well served too - with lists of endemics, key sites to see each one, suggested itineraries and the like.
A worthy investment for your trip!