This was a great reference book for the Dark Tower series. This series is extremely complex and incorporates many different books, even outside of the main 7 Dark Tower books. I was able to understand concepts that were vague or only quicky explained (Eg where does the portal of the bear lead to?).
This book catalogues characters, places, Mid-World sayings, and more. In the main sections, book and page numbers are referenced, enabling easy look-up.
One of the things I wish this book would have done is include ALL Dark Tower related books (Insomnia, Black House, Hearts in Atlantis, etc). And because those books are so vital to the story, it definitely feels like this concordance is lacking several entire and important Dark Tower books.