All in all, in my 3 years living in Belgium, I found this a really helpful guide book. Prices are always wrong in guidebooks, but I found the contact information (web, address, phone) nearly always right, and the descriptions accurate.
You will be very challenged to find another guidebook that has this level of coverage of Belgium in its entirety, as most seem to focus on Brussels, Gent, Bruges, and perhaps Antwerp. Belgium seems to typically be an afterthought on most tourists' itineraries.
I really enjoyed the author's picks, both hotels and restaurants. What can I say to the other reviewer where the hotel unfortunately cancelled their booking because they found a group that would pay them more? Is that the authors' fault? No, welcome to Europe, and to Belgium, where the customer is always ... wrong!!
So you're browsing guidebooks, and wondering which one to get?
I would have to say, based on my experience using an earlier edition of this book for the past 3 years (I imagine they're pretty similar!), if you're swinging through Belgium for 2 days, and going to see Brussels and Bruges, this book is probably not the best for you. You'll probably do better with a thinner city-specific guidebook. But if you're going to tour around Belgium, or spend an extended amount of time in a city or two, then the in-depth coverage of this book is a real benefit.
One criticim I do have to echo: Lonely Planet, let's face it, is not known for its maps, and this book is no exception. They're good enough, and I've never NOT been able to find something, but sometimes the maps, er, well, don't necessarily reflect reality.
So all in all, this is a solid book, and if you follow my advice in paragraph 5, I think you'll be happy with it.