As Roget is to Thesaurus, so the Ahearns are to books. "Collected Books" is a massive listing of values for tens of thousands of books. Collectors will find the never-to-be-obtained rarities listed (entertaining to look up) but also the more attainable first editions in the $50-$500 range. This is a big book to lug along to a sale but, believe it or not, an enjoyable browse and a fine way for the aspiring collector to see which authors are more collectible.
This book is NOT three things - reminders that the serious collector must, inevitably, accept the need for a number of references which will have some overlap.
It is not a guide to identifying first editions - often a challenge for the large number of pubishers who do not clearly indicate 1st ed status. For this I'd highly recommend McBride's pocket guide. It also isn't really a guide to "modern" first editions, at least those that are in the $30-$100 value range. You may find Uris or Ludlum's first two books here but not their 3rd or 5th. It MAY make a difference to you whether such a title is really worth the $30 a dealer is charging. For these books I recommend Lee's "20th Century First Edition Fiction." It is not merely a listing of authors' first books, although it includes those... for that, and a wider range of midprice authors, their "Book Collecting 2000" is great. .....
Once you know what the book is not, you can determine if it is for you. The five-star rating applies to those buyers with a serious interest in collecting (or thinking about collecting) the roughly 20,000 most valued books. It includes all the good stuff. Where necessary it lists details of first-edition "points", the subtle details of identification that, for some books, distinguish earlier from later states. Alternate editions such as American and UK or limited or special editions are also priced separately. It is a useful, even entertaining, reference for the serious collector. Someday the online databases and search engines may supplant references like this (I do use them more often) but if you're a bibliophile your prime reference on books just has to be a book.