I gave this product a four-star review in October 2008, taking off one star for the quality of the scan. That issue has been fixed, so I am giving this product the five stars it deseves.
The Creature Catalog adds 150 monsters to BECMI D&D which aren't in the Rules Cyclopedia. (including early versions of the Neh-Thallgu/brain collector, the choker, the mimic/polymar and other favorites)
The best parts of this book are the new wilderness encouter tables and a comprehensive index of which creatures are located where. This saves a lot of book-flipping and frustration.
The Creature Catalog and the Rules Cyclopedia are the only two books you need to run an real old-school campaign of D&D.
[5 of 5 Stars!]