In general, Western Australia still seems to be off the usual tourist path for most outside visitors to Australia, so there wasn't much selection when it came to finding an appropriate guidebook. For the most part, guides seemed to be too broad (covering all of Australia), or too specific (focusing just on Perth). Despite being an absolutely enormous place on its own, few choices seemed to address the state of WA.
We picked this book up out of desperation, but for the most part, it did a decent enough job. In typical Lonely Planet style, there were lots of budget options for food/accommodation and plenty of details on tours and logistics. Most of the information appeared to be accurate, and a few tips proved quite helpful.
My biggest qualm with book is that its layout centers around towns, and in such vast and spread-out areas, a town-by-town approach isn't the most useful. Many of the smaller towns have few attractions or amenities, and nearly all of the must-see destinations (national parks, wineries, caves, capes, coasts, etc) lie in between these small towns.
Finally, despite the extensive use of flowery adjectives, the descriptions of individual sights often remain vague. For some of the national parks especially, the description seems to be just a list of key points copied from a park map or guide, sometimes with no description whatsoever.
In the end, it did prove to be a useful aid to our tour of the southwest and south coast of WA, but we definitely needed to augment it with some of the literature and information from the local tourism agencies. It was certainly better than nothing, but hopefully further research will lead to some improvements in later editions.
One possible alternative is West Coast Australia (Footprint West Coast Australia), which seems to have better descriptions of some of the southwest parks but covers only the western edge of the state.