Belial's Brood is a diabolist Covenant that likely plays the role of adversary in most chronicles, and as an antagonist book, it works well. Beyond that though, this book was certainly the most interesting of the Covenant books, and the material makes for very exciting reading and gameplay. Another storyteller and I devoured this book, and quickly built a chronicle on our enthusiasm for the covenant - the best chronicle our troupe has run to date.
For those familiar with Vampire: The Masquerade, the Brood aesthetic falls somewhere between the Baali and the Sabbat. They practice the vaulderie, which forms the crux of member relationships and is backed by a dark spiritual Pursuit personal to each member. Much as the Invictus draws many of its ideological underpinnings from the Ventrue, the Brood is heavily influenced by clan Gangrel, more specifically its connection to the Beast. The covenant has several factions or sub-cults, which each have their own creation myths (for lack of a better term), favored aspects, and preferred means of corrupting the world.
The book's storyline follows a member of the Ordo Dracul in researching the covenant, only to become entwined in its seductions and join. As far as sourcebook fiction goes, it flows well with the source material and makes for an interesting read. The covenant's unique powers, called Investments, are varied, diabolical, and cool. Examples include the ability to call blood to the character, the power to make one's limbs act independently of the body when removed, and the means to permanently move one's soul into the body of another living vessel. There are a handful of new Devotions that incorporate these powers as well.
As the basis for roleplaying a group of Brood characters, this book is excellent. Readers will surely find powers, myths and factions that appeal to them, beyond the obvious draw of being a bad guy with utterly no concern for Morality. As I mentioned above, it was incredibly satisfying to play, and the vaulderie entirely eliminates the bickering and backstabbing that so often accompany roleplaying a cosmopolitan coterie.
Having read all the covenant books but VII (which, based on what I know about it, I never will), I feel safe in saying this is the best of them. Whether you're looking for antagonists, a fresh feel to a new chronicle or just a good read, you'll be happy you own this book.