As I moved later in my 3.x/d20 games, Demons became major antagonists for the characters. This book was one of many I bought on the subject, but one of the better ones. The book begins with a a couple of new races for PCs based on Monster Manual/SRD races, the Steward Archon and the Aasimar. Next we go to a discussion on how each of the core classes can be a "Demon Hunter" using what they already have. I lked this part since it also encourages better role-playing.
We follow up with demon-hunting prestige classes, which are a better sort than other books like this one. My favorite was the Righteous Sword and his power "A Good Man's Wrath". Very nice.
Chapter two gives us the options; new feats, new uses for skills and new spells. As well as new equipment. All of which have had a place in my game at one time or another.
Chapter Three gives up campaign advice and how to keep a demon hunting game going. I particularly like the Urban adventures parts since I love to play in cities and there is not much in the way of good material out there.
Chapter Four (which thematically could have been just more of Three) gives us the organizations that fight demons. After years and years of playing horror games this was less useful for me, but good for someone just getting into the demon-hunting RPG biz.
Chapter five gives us the monsters. Not very many here and other books do have better choices, but I don't think that a huge list of demons was the prime motivator of this book; so that is fine.
All in all a good book and a very nice collection of demon hunting ideas for any group of characters.