Elder Evils is one of the last few 3rd edition Dungeons & Dragons books and due to the publishers focus on the newer edition, this book feels unfinished and is missing much of the stuff common to 3e books.
The focus of this book is "End of the world" evils, like Cthulhu and the Four Horsemen of the Apocalypse. Chapter one is a basic guide to "So you want to end the world" and Chapters 2 - 10 are different "Elder Evils" you can unleash.
The book provides plenty of new ideas and opportunities, but what is missing is from the book is the basic rules for incorporating these ideas. There are very few new feats, most here are reprinted from the Book of Vile Darkness, and there are no new spells, prestige classes and only two magic items. It is like a cake without any icing.
The art is good, not recycled, but the book is a fixer-uper. You are going to have to do much of the work to actually use these Elder Evils. Each Elder Evil chapter does include stats for the Aspect of that Elder Evil, some example minions and a short adventure to try and stop it. The adventure is presented in the newer spit format, with the text on one set of pages and the encounter on a different set of pages. Personally I find this very anoying and difficult to use, I prefer everything together in one place.
Overall, it is a good read and has lots of good ideas, but since the writers leave adapting most of those ideas to the DM, I only gve it 3 stars.