The Dummies series is known for providing practical, easy to understand information to get you started on any topic. The Dummies book for Hawaii does this same thing - black and white, highlights, with short descriptions.
It's important to understand this. This book has quality information - and they are helped out by the Frommer's team, so you are getting Frommer's advice here in the book. However, there are no lush full-color photos to help you absorb the beauty of Hawaii. There are not turn by turn directions to get to those secret locations like the Southernmost Point in the United States.
The book does shine at what it provides. If you're looking for hotels, other travel books often skim over this information. The dummies book provides price ranges, 'best' choices and explains exactly what to look for based on your needs. You get phone numbers, website URLs and details about parking and specials.
The same is true for restaurants. You're told what items on the menu are worth ordering, what seats give the best views and what is great for romantic couples vs for families. Often you are just on a given island for a day or two and don't have time to figure these things out for yourself. Following the advice can make the difference between a so-so dinner and an evening you will remember for a lifetime.
The book in general is a great reference for people who are going to stay on land, with its heavy emphasis on hotels and restaurants. People who are cruising will find it far less helpful. It's description of the famous black sand beach on the big island of Hawaii is super short. The Southernmost Point gets 2 sentences and you aren't even told how to get there. The book is thick - but all in black and white, so you miss out on the gorgeous atmosphere of Hawaii. You learn how to find a good taco, but not the meaning behind the location you are visiting.
So I'd suggest this book primarily for people who are staying on land, and make sure this isn't the only book you get. Go through this book to choose your hotels and restaurants, but get another book or two to go into the background of the location and to map out the sights you wish to see.