CULTS OF THE BLOOD GODS is a somewhat controversial topic to begin with as it is a book that reflects Kindred (vampire) religion. One of the elements that makes V:TM so interesting is that it doesn't shy away from presenting a dark Christian mythology-flavored universe where God cursed Caine only to have said being spread his curse across Abel's descendants. This has not always sat well with atheist or other religious gamers and is a topic some prefer to be left out of their power fantasy of bloodsucking monsters.
I personally have always loved the occult aspect of the World of Darkness setting. Speaking as a liberal Christian growing up in the fundamentalist Bible Belt, I've enjoyed the satirical element of the setting as well as its hidden mysteries. Cults of the Blood Gods doesn't just focus on the Caine myth, though, and expands significantly on the options for those who wish to play polytheistic, pagan, drug, ancestor, and other forms of religion cultists.
A warning for those who are reading this book in hopes of getting new material for the Sabbat, the largest Blood Cult among vampires, that this book doesn't contain any information about that organization or rules for Paths of Enlightenment. While it does offer some options for inhuman convictions, the book is primarily devoted to other cults as well as updating the Giovanni as well as Cappadocian Clans to the modern era. Personally, I'm content to wait for the Sabbat to get their own recently-announced book.
Its difficult to pick out the best parts of the book so I'm just going to list some of my favorite elements of the new cults presented as well as give some short thoughts:
* The Church of Caine: I've always been a fan of the Cainite Heresy and hated how the Sabbat had warped our vampiric lord, the First Murderer's, ministry. This provides a revival of the organization with some hints of Sabbat defection. It also provides a coherent mythology for the undead as well as an updated to the Lure of Flames Path as a pyrotechnic set of rituals.
* The Church of Set: The Church of Set and Ministry split was confusing to me so it was nice to have it spelled out to be an ideological conflict between the Set purists versus the polytheistic chaos worshipers of the Clan. The Church of Set are fundamentalists of a religion devoted to freedom and that is an interesting twist to me. They're also archenemies of the Church of Mithras as well as Ministry.
* The Cult of Mithras: I've long been a fan of cult favorite, Mithras, the 4th generation Prince of London. This expands on his in-universe cult and adds plenty of new rituals as well as world-building for those who want to use him as background flavor. Mithras, himself, is probably dead as of The Fall of London but that doesn't mean his cult doesn't live on. I also like how he's set up as another archenemy for the Church of Set (alongside the Children of Osiris, Kemintiri, Mummies, and Silent Striders--guys are hated worse than the Tremere).
* The Nephilim: An interesting character from the Dark Ages was Michael the False Archangel of Constantinople. The Nephilim are what remains of his cult and they are the most Toreador that ever Toreadored. They're arrogant, beauty-obsessed, obnoxious hedonists that are basically Toreador + another Toreador. I don't think they'd let the Nosferatu into the club, though. That's just not their bag, IMHO.
* The Dread Cult of Eligos: I'll be honest, this is probably my favorite of all the cults in the book and one that I want to use in my next Chronicle. It is a Satanic cult of blood sucking lunatics who are worshiping a vampire methuselah. Except not. It is a front for the Second Inquisition that has gotten completely out of control.
* The Sevitors of Irad: I've always liked the Servitors of Irad ever since the Elysium supplement. They were eventually expanded into a group allied with the True Hand. This group write-up doesn't mention the True Hand but I'm inclined to think that's because they're still rebuilding/being co-opted by the Baali. I love Antediluvian worshipers is all I'm saying.
The biggest part of the book is the update of the Cappadocian and Giovanni bloodlines. The Harbingers of Skulls, Samedi, and Nagaraja are all merged together via a mystical rite with the former to become the Hecata. Augustus Giovanni has apparently been destroyed and many of his closest cronies have been assassinated but the majority of the Giovanni clan remains intact. It is more a reorganization than a genocide.
I honestly think the book went a bit overboard with the mystical binding but I think the Hecate being a micro-sect akin to the Camarilla of the "Necromancy" clans is a pretty cool idea. The Nagaraja may not be related to the Cappadocians but them joining together with the Harbingers after the Black Hand's destruction is a pretty good idea. I also like the greater focus on the Giovanni branch families versus the debased Italian banking clan.
Rule-wise, there's a lot more here than in Chicago by Night. We have the rules for creating Hecata characters as well as expansions on how to use Oblivion in your chronicle. Not everyone liked merging Necromancy with Oblivion but I think it works well. We also have information on the aforementioned Bloodlines and some cool Loresheets. The sourcebook also contains a cool little chronicle called "Styx and Bones" that is about the resurrection of a Cappadocian Elder gone horribly wrong. I'm a little nonplussed by, "wait, people can be raised from the dead in the setting now?" However, it's a pretty great story all round and I will eventually run it.
In conclusion, this is a fantastic supplement that is a must for any campaign that wants to deal with extreme religion in Cainite society, the Giovanni, Cappadocians, or the Underworld. It's probably better if you're going to run an all-Hecata Chronicle but I also think that it's perfect for those who want to play one of those pale medium types.