I bought this book last year, a few short weeks before our annual camping trip - this time to New England - because the free AAA campground "guides" we used the year prior were awful and featured mostly sites catering to RVs.
I must say, we found the reviews in the book very helpful, and it did lead us to some wonderful spots in campgrounds we might not have otherwised discovered. However, having only learned about these great destinations a month before our trip prevented us from securing some of the most beautiful spots. My recommendation, therefore, is to plan ahead, far, far in advance, if you want to experience the best sites New England has to offer. Otherwise, you will arrive only to find out the spot you want has been booked.