A 31 page book (excluding cover, credits, and license), this describes a range of masks, from the mundane to the magical. The artwork is basic, but the book is well written, and includes a great variety of items. It begins with a list of twelve types of standard mask, which serve as a starting point for the later discussions, as well as an expansion to a typical equipment list.
After that, there are seven alchemical or mechanical masks, most of which duplicate more advanced technology (gas masks, diving masks, etc.) These are relatively cheap, and could well be useful, if your campaign allows such things - they could alternatively be replaced by something that uses simple magic to achieve its effects. Finally, there are sixteen magical items based on the mask theme, ranging from CLs of 3rd to 10th. With many of these, the fact that the item happens to be a mask is just a cool effect (albeit one that lets you the face slot for things you normally wouldn't), but others are directly linked to disguise, altered personae and the like.
The book rounds out with a description of a mask shop and its owner, which is well written, but fairly standard as shopping locations go.
All in all, I liked this book; it's an original idea for something a bit different, and easy to place in any campaign world. Some might prefer higher production values, but I can see this being useful enough that I'll give it 4.5/5.