The biggest update to the setting is the book finally provides rules for the Tzimisce, Ravnos, and Salubri clans. One of the biggest complaints about the initial release of Fifth Edition was the fact that it only provided rules for the original seven Camarilla clans as well as Thin Bloods. Later supplements added write-ups for the Ministry, Banu Haqim [Assamites], Lasombra, and Hecate [Giovanni]. I always felt this was one of the Fifth Edition's biggest issues as Vampire: The Masquerade 20th Anniversary Edition provided rules for all thirteen clans in the main book.
As a long time fan of the Tzimisce, I was really appreciative of their write-up. I felt the absence of the Sabbat was another flaw of Fifth Edition and it was impossible to adapt them for my games because I didn't have the rules for its two Clans. I like the remake of the Fiends, focusing more on them as vampire-shaped dragons consumed with greed as well as wrath versus sadistic Buffalo Bill-esque psycho killers. Their new version is heavily influenced by the Dark Ages interpretation of the Clan and I like that a lot. I've always felt the more overtly "gross" Tzimisce were inferior to the voivodes of old.
The Ravnos update is something I'm a little iffier on because I already felt the Clan had already been "fixed" by playing up their Indian subcontinent roots. I've always felt V:TM should be more international and incorporating the Rakahasa myth felt like it expanded the story significantly. The new versions of the Ravnos are a more regionally neutral "Trickster" Clan that exist for the purposes of robbing from the rich and laying low the haughty.
The Ravnos are also possessed of a much better Clan Flaw this time around: being unable to stay in one place rather than having to commit crimes (that plays into unfortunate stereotypes). Even so, I feel like this infringes on my favorite elements of the Malkavians as the Trickster Clan as I was one of the few people who took their position as the pranksters of Kindred society seriously. Still, I think this version of the Ravnos is likely to stick and fits the more universal Clan approach that V5 seems to be going with.
One thing I liked about the treatment of the Ravnos is that it establishes the Week of Nightmares did occur and the Clan is a shadow of its former self. The consequences for the previous metaplot aren't glossed over and weigh heavily on the Clan. It makes you wonder if trying to destroy one's Antediluvian is even worth it given the horrifying results. Then again, the Hecate seemed to have gotten away with it so maybe the lesson learned is, "Don't nuke your Antediluvian. He'll take it personally."
The Salubri are kind of an odd pick for the third Clan as while they're historically important, I'm not really sure anyone was overly clamoring for their return. At least over any other Bloodlines. On the other hand, I actually feel like the Salubri may have been the Clan most improved by its update. Previous versions of the Salubri have leaned hard either into them as vampire saints or deranged fundamentalists. Obeah was also something of a gamebreaker, even though you can still replicate most of the powers here. They're now restricted to vampires and can't be used to heal humans of physical injury.
The new Salubri having the relatively normal discipline spread of Auspex, Dominate, and Fortitude means that they're significantly more usable in a "normal" campaign. While they still have the Clan Flaw of Hunted as well as their Third Eye, I could easily see these Salubri staying hidden for centuries without their Discipline outing them. Their previous Clan Flaw of being unable to feed from the unwilling also made it hard to tell horror stories, which defeats the purpose of the game. The write-up seems to imply the Salubri numbers are tiny, though, and I was hoping we'd get around that. The Tremere undoubtedly exterminated them in Europe but there's plenty of other continents for them to have fled to.
The book also provides a nice little section on coteries that explains why vampires choose to band together when they're normally solitary creatures of the night. I really enjoyed this part but don't have much to add other than its good flavor text. The book also provides updated rules on ghouls and talks about the challenges of roleplaying consent when dealing with the fact that they're inherently a master/slave relationship. I appreciated this discussion and the maturity with which it's handled. People come to vampire to play horrifying things but it's important to understand what your players are comfortable with.
The additional rules and Disciplines that the book provides are okay. A lot of fans are going to be annoyed at the apparent nerfing that Vicissitude, Chimestry, and Obeah have all received. Vicissitude is now a subset of Protean, Chimestry of Dominate, and Obeah of Auspex. The fact Salubri cannot heal physical injuries anymore is something that is probably a wise decision for game balance but still is a huge change. Presumably any actual healers were Blood Sorcerers or possessed of Vicissitude Protean variants.
Overall, I was very fond of this book and it provides a lot of useful material for Fifth Edition. I'm going to be honest that I probably think this should have been part of a Player's Handbook. On the other hand, it's hard to argue with free as a price tag. The information on the remaining Clans, mortals, and ghouls opens up a lot of options. I also approve of the majority of updates. Some people will be off-put by the changes but I think it makes all three Clans much more playable in mixed coteries. I also think the rules for ghouls, coterie rules, and role-playing suggestions are very helpful.