As the title suggests, this is a thorough examination and reworking of beings with the Fey template for D&D3. For those looking for crunchy details, there are plenty here, with feats, character classes, races, spells, and monsters all provided. The races and classes are not overpowered, making them easily adaptable.
The best part, however, is the detail on the culture and nature of the fey. Some of this departs from the standard MM information (these fey, for example, do not need to eat or sleep), but that's easily adapted if you really feel the need to stay consistent. What it does provide is a feel for the fey as truly alien beings, and as something much more than the standard dryads, satyrs, nixies, and so forth - while still encompassing all of those.
The book really brings a touch of folklore to a D&D game, making the fey more than just strange monsters or a different culture, and does a good job of explaining why the fey act the way they do. It does introduce a large number of new concepts, making it of more use for a campaign that heavily features the fey than one with just a few casual encounters. But, for such a campaign, it does seem invaluable, and highly original.
With good layout and high quality artwork, this book is well worth the price.