The idea here is to provide all the essentials you need for the most popular parks in the West - places to stay, where to eat, and what to see - in a compact and affordable package... and in that, I think they succeeded. I've always prized the Frommer's guides for their opinionated, but fair coverage, and that's intact here. There's also a variety of hikes for all ability levels (my personal favorite way to experience our parks), each rated 0-to-3 stars for scenery - always good to have, and hard info to find otherwise.
Driving times are provided for the parks covered, but as another reviewer mentioned, Crater Lake NP is not (a strange oversight, in my opinion, and one of the few negatives - feel free to treat this as more of a 4 1/2 star review). Other national parks not covered are North Cascades in Washington; Black Canyon of the Gunnison and Great Sand Dunes in Colorado; Theodore Roosevelt in North Dakota; Lassen, Channel Islands, and Pinnacles in California; Great Basin in Nevada; Saguaro and Petrified Forest in Arizona; Capitol Reef in Utah; and Big Bend in Texas (I believe Wind Cave in South Dakota and Guadalupe Mountains in Texas get mentions, but not full coverage). These are smaller, less-visited, and/or less-accessible parks to be sure, but omissions nonetheless.
Still, if you're planning a grand tour of iconic parks and spending a day or two or three in each, this book will get you there. It's easy to tote around and it's a pretty decent deal. If you're spending more time in a given park, though, you'll want something more - "Your Guide to the National Parks" is a good multi-park alternative (but bigger and heavier), and there's tons of in-depth guides out there for Yosemite, Grand Canyon, and Yellowstone - I personally like Lonely Planet for comprehensiveness, and the Moon or Falcon guides for hikes.