It's easy to see how this happened. Blood magic is the signature Tremere ability. They're the best at it, and it's the thing they're best at. So you couldn't have a book about blood magic and not talk about the Tremere. However, they're only one clan out of 13, so to the degree that Thaumaturgy is a Tremere-specific thing, it belongs in a Tremere-specific book. You wouldn't really want to do a full supplement that was only useful to 1/13th of all player characters.
And in this book's defense, chapter four, about non-Tremere blood magic is great. The Followers of Set wield ancient Egyptian sorcery powered by the divine spite of their namesake. The Assamite clan of vampire assassins is aided by a secluded cadre of elder sorcerers who drink the drugged blood of their servitors to gain mystic visions that reveal the vulnerabilities of the clan's prey. The Tzimisce of eastern Europe call upon the ancient tradition of the koldun to wield the elemental power of their homelands. All of these guys, plus the Tremere, could definitely use a book that expands their fell powers and suggests plots, settings, and characters that put sorcery at the foreground of the story.
Unfortunately, this book is not quite that. It has elements of it, but it doesn't seem to recognize the advantages of cross-pollination. Each branch of sorcery is powered by its own carefully-guarded Discipline (so that Setite, Assamite, and Tremere sorcerers each call upon a different trait) and each one has its own set of Paths and Rituals. I think, in practice, you'd probably say that it was okay if a koldunic sorcerer wanted to learn their own version of the Hearth Path or the Court of Hallowed Truth Ritual, but the book does not directly come out and say that it's possible.
Which leads to a chapter 2 that is ostensibly about the theory behind blood magic, but which mostly talks about the Tremere's Hermetic occult philosophy . . . and the Tremere's internal hierarchy . . . and the Tremere's network of chantry-houses . . . and the experience of apprenticing to a Tremere. It's all welcome material, but it's not what I signed up for when I picked up a book promising the "secrets of thaumaturgy."
I can't help dwelling on a passage from the introduction:
We've made the attempt to move beyond the obvious "book of spells" concept. In fact, of this book's many words, only half are devoted to game systems and new powers. While this no doubt put the book into the "that sucks, I wish it had kewl powerz" column for many people, those who are looking for storytelling hooks for their chronicles shouldn't be disappointed.
Aside from being a classic example of White Wolf writing a book and then inexplicably daring you to enjoy it, the thing that strikes me about this passage is that its prediction is wrong. I'm actually largely satisfied by the book's cool powers (I don't know what to tell you about that sarcastic spelling, it was a thing in the turn of the century White Wolf fandom and the developers sometimes encouraged it, contrary to their own artistic and commercial interests), but I was indeed disappointed with the storytelling hooks.
Like, there's a section about summoning ghosts and demons, and it's written from the perspective of a rogue Tremere, who talks about the utility of spirit magic, the occult theory behind it, and vaguely about its risks. And that's instead of the out-of-character section we could have gotten about spirits' personalities and motivations, different possible arcs for a summoning narrative, or a sensual description of the rituals themselves. That may just be a weakness of the fiction-driven approach, though. It doesn't have room to treat "storytelling hooks" as a tool for storytellers, because the storyteller doesn't exist in the context of the narrator. Chapter 4's encyclopedic approach does offer some useful hooks just by being open-ended and factual. The revelation that Setites can desecrate cryogenically stored bodies in lieu of increasingly rare Egyptian mummies does immediately suggest a possible plot.
But the thing that bugs me most about the introduction is its false dichotomy. It doesn't seem to realize that the cool powers are the storytelling hooks. You've got these sinister undead intellects, driven by obsession, willing to endure danger and privation and humiliation for decades on end in the hopes of unlocking the profane power of the blood . . . so tell me about the prize. Tell me what they are going to do with it. Tell me what's at stake if the players cannot stop them (or, more likely in a villain-protagonist game like Vampire: the Masquerade, if they're not stopped by a group of unlikely NPC heroes).
The description of the Court of Hallowed Truth ritual includes the line
Several princes have come to rely on this, much to their undoing, as either the prince becomes preposterously indebted to the Tremere or other Kindred resent his heavy-handed tactics and refuse to attend meeting. This power invariably erodes the power of princes who rely on it, though some are too short-sighted to understand it.
What's that, a storytelling hook inside one of the kewl powerz? More plot in two sentences than the entire two and a half pages about Tremere Chantries? Because "the power to compel truth inside a magically-prepared chamber leads to resentment and chaos in the deception-driven world of vampire politics" is a great elevator pitch for the game's starting situation? I was led to believe that mechanics and story were incompatible.
Although, don't read too much into my sarcasm here. I expect that a lot of this book's weakness can be laid at the feet of the short turnaround time of early 00s rpg supplements. My guess is that Blood Magic: Secrets of Thaumaturgy went from pitch to publication in less than 3 months and that's why it has nine credited authors. This really needed to be one coherent book whose sections built off each other and which advanced a concrete, specific vision for blood-magic-driven campaigns, but it probably had too many cooks to ever really be that. In the end, it winds up being a halfway decent book of spells.
Ukss Contribution: The Necromancy section has me super sweating the upcoming Clanbook Giovanni. I won't disturb you with the specifics, but the phrase "after that, the Giovanni will have to come up with something really perverse" is used in reference to them trying to top a super fucked-up bit of necrophilia.
However, that section also contains my favorite detail in the entire book - the modern update to the Authoritative tradition in western necromancy. Instead of crowns, robes, and scepters, modern Giovanni impress the dead with "Rolex or Cartier watches, money clips distended with high-denomination bills, mahogany office furniture or expensive designer clothing."
This bit of imagery amuses me to no end. A sorcerer trying to impress a ghostly rube. "You want to do what I say, look at my fat stacks of cash." It's silly, but in a way that I unironically enjoy. The Giovanni as lifestyle influencers, selling the sigma-grindset hustle to the damned. I'm going to try and figure out a way to make it work in Ukss.