This book is a collectors gem. While there is the new 3rd edition books which are admittedly better, the book is still very good. It contains everything a DM who owns the other books for this edition needs to run a fun encounter to keep the PC's on their toes.
It has a wealth of good pictures that really convey a good sense of the monsters looks, good for inspiring fear into the hearts of the players of any game.
The other advantage it has over later editions is the inclusion of random monster tables in the back for unexpected encounters. I personally use this for a good one-on-one fight called a "Gauntlet" when the DM is away.
The price for this book is still slightly high considering the new edition books don't cost much more but it is not a major set-back.
Fully worth it, this book is a joy to use and helps the new DM with easy to use headings. The fact that the book is available on Amazon is a marvel considering it's age.
This book is a very useful and good book which is only held back by the more recent 3rd edition and 3.5 edition books. Highly recommended.