For me, I've always been a fan of the Sabbat and they are my second favorite sect after the Anarchs. I've played many interesting and fascinating Sabbat characters both as a Storyteller as well as a player. I feel like if there's any gameline that shouldn't judge you for being "evil", it should be Vampire: The Masquerade. Nevertheless, that doesn't automatically discount my interest in this book. I feel like the Sabbat are something the setting desperately needs to be complete and even if I have to make my own rules for playing them, I want as much as I can about them in Fifth Edition. So does the book succeed on that level?
Thankfully, yes. This is easily the best of the main game books, surpassing both sect books as well as the main book, IMHO. I prefer Chicago by Night Fifth Edition and Cults of the Blood Gods but this is definitely one of the better works done for Fifth Edition. It is written almost entirely out of character and gives clear, concise, as well as informative facts about what the state of the Sabbat is as well as how to run them. There's also ample crunch to be found here as well as lore. The book is more than a little on the short side, though, with 134 pages in length. Given the Camarilla was 204, I have to wonder who decided to not give the writer room to breathe. I don't think anyone would have disliked having more material to follow up on.
The Fifth Edition version of the Sabbat has suffered heavy losses at the hands of the Second Inquisition, their massive Gehenna War, as well as civil war. The Sabbat has forfeited most of its territory to the Camarilla and Anarchs with defectors to both sects. Some of the more popular Paths of Enlightenment have also become forgotten with the Path of Beast (Feral Heart), Honorable Accord, and Lilith being all but abandoned. 5E amalgamation has also hit a few of these paths too with the Path of Night and Path of Metamorphosis becoming "flavors" of the Path of Cathari and Path of Death and Soul. There is no Regent of the Sabbat and it is controlled by a loose alliance of warring Cardinals. No sign exists of the (False) Black Hand special forces that once were the deadliest killers outside of Alamut.
However, not all is ill in the Sword of Caine. The Fifth Edition version of the Sabbat is more ideologically committed and united than ever. No Sabbat remain on the Path of Humanity and infighting is practically nonexistent. While they have lost vast swathes of territory, they still maintain Archbishopdoms and strongholds across the world. They do not suffer Stains, have Touchstones, or have penalties for diablerie. Oh and among their tricks are now the ability to raise feral zombies, create Blood Brother-esque mini-vozhd from ghouls, and other abominations against both magic as well as reality. The Gehenna War is all but it is not fought in the Middle East but every corner of the globe against anyone the Sabbat wishes.
The Sabbat is not a swarm of locusts even if their focus is entirely on the war against the Antediluvian. They engage in hot war of Mass Embraces, mass diablerie, and Sabbat Crusades as before but this is only part of the way it's done. Instead, they also engage in cold war using subversion, destabilization, and infiltration that is every bit as intelligent as before. The Paths replace Clans for dividing up the Sabbat with all of them identifying as antitribu now. We get insights into the various ritae the Sabbat perform as well as how each Path treats the process of doing so. We also have a new Path in the Path of Sun that is followed exclusively by the Thin Bloods that may actually have a better time in the Sabbat than the Camarilla.
The art of the books is fantastic and those few fiction elements of the book are well-handled. I was disappointed we didn't get more information on Sabbat NPCs but Lucita is apparently (accent on apparently) still unalive and ruling Madrid. She's now a Lasombra Antitribu. Vykos is also alive, back to referring to themselves as Sascha, and a Tzimisce Antitribu. We also get a part of the book detailing what happened to the Web of Knives and Alamut. It's ridiculously gonzo and I think meant to state we're never going to hear of Ur-Shulgi or the diablerie-happy murder cultists of the Banu Haqim again.
In conclusion, this is a solid and entertaining book but I can see where massive amounts of content could have been added that would have made it an even better experience. They could have easily included a Path system and mechanics for running them rather than just say, "Sabbat don't suffer your puny degeneration unless they are nice to mortals or are other kinds of freaks." The seeming loss of the Inquisition and (False) Black Hand is also notable with no commentary on the Harbingers, Salubri Antitribu, or other matters that could have been inserted into the abbreviated history. There are also no Loresheets, even for people who fight the Sabbat or have defected from them. But for what the book is, sharing a truly terrifying fanatical sect that will not be stopped, it does gloriously.
Note: Sabbat: The Black Hand is not presently available in printed form but the PDF is available at a somewhat overpriced $35 (especially for the page content) or free with the purchase of the physical book that is only ten dollars more. I recommend getting the latter if you're not going to wait for the price to go down as at least you'll have more bang for your buck. Even then, the physical books haven't been shipped and you just get the PDF immediately. This will, of course, change with time.