I picked this book up somewhat reluctantly - my budget for D&D books is pretty tight - but I'm glad I did. The title is misleading - it's an EVERYONE Guide to Eberron, and if you like the setting, this book is a definate must-buy. My only complaint is that it was too short.
Because Wizards of the Coast limited the book to 160 pages [in line with other, similar releases], there just wasn't enough space to cover everything I wished this book had covered. For example, the Five Nations get a 2-page spread, the Demon Wastes get 4 pages, Droaam gets 52 pages, the Eldeen Reaches get 4 [but that also covers Druidic Sects], The Mournland gets 2 pages, Q'Barra gets 2 pages and Valenar gets 6 pages [including a new prestige class] - but Aundair, Breland, Karnath, the Mror Holds, the Shadow Marches, the Talenta Plains, Thrane and Zilargo, DON'T get their own entries - and they should have. Sure, they get a *little* coverage under other entries, but I would have appreciated a more thorough overview. The information on the other continents and the oceans of Eberron is terrific.
But WotC cut out *everything* that can be found in other references, so this book is almost 100% pure new material - which is its blessing and its curse. If the encyclopedia-style layout bothers you, there is an excellent Index in the back of the book [which is too often missing from WotC products] in addition to a detailed Table of Contents. The book is fun to browse through, and it's easy to find a specific piece of information if you need it.
I especially like the way this book ties together supplemental game stuff into Eberron. Use any of "The Complete..." books and you'll find suggestions for where the new core classes and prestige classes will work. Races for the "Races of..." series find out-of-the way homes in Eberron - so if you use those books, they're covered - and if you don't use them, you lose nothing from the game world. The book is worth the cost just for that help.
I would have been willing to pay more for more content, though - especially if it were of the same quailty as what was included. That is the only reason I rated this book at 4 stars instead of 5. Actaully, I think it deserves a 4-and-a-half.