I'm going to have to be careful. The Complete Book of Necromancers is very good, and I'm going to be tempted to use that as an excuse to indulge in full-on anti-AD&D snark. It would be easy to smirk and say that this feels so much better than regular Dungeons and Dragons, but that would be ignoring the fact that this is, indeed, a supplement for AD&D 2nd edition, and thus by definition part of what AD&D is.
In my defense, this book feels like it's at least a decade ahead of its time, more akin to what White Wolf was doing with the New World of Darkness than anything its contemporaries were doing (as part of AD&D or otherwise). It still has some obnoxious D&D-isms. The sections about finding attributes for and applying dual-class mechanics to your NPC villains were weirdly rules-focused, as if the DM were obligated to follow the character-creation process and could only create adversaries that could theoretically be PC-legal. Yet there's something else at work here. There's an awareness of genre, and the implication that you could be doing this fantasy stuff on purpose.
It's something of a misnomer to call this The Complete Book of Necromancers. Necromancy is a running theme. It informs all the new spells. But it isn't really what the strongest parts of the book are about. A more accurate title to this book would probably be "A Guide to Sword & Sorcery, Pulp, and Gothic Fantasy."
Yes, there's necromancy involved, but the magic in this book is more the sort that is wielded by decadent sorcery-kings languidly sitting on the jewel-encrusted thrones of decaying jungle kingdoms. Or reckless natural philosophers, probing the forbidden limits of human knowledge and driving themselves mad with things man was not meant to know. Or, you know, there's like this creepy blood-soaked clown who sneaks up on you with a mad cackle, but you look past him and you see something shapeless lurking in the shadows and you know that's the real threat.
It's all just magic. Necromancy is the excuse, because it's a school of magic that never quite fit in with D&D's morally-neutral function-first approach to spellcasting. But the main thing that focusing on necromancy accomplishes is to allow the book to explore a magic system tied to a different set of genre assumptions.
There's a list of appropriate kits from other supplements that suggests the Witch kit from The Complete Wizard's Handbook would be good for necromancers. In just a few sentences, it does a better job selling the kit than the wizard book did in a page and a half. I'd attribute that to a greater appreciation for the literary and mythological antecedents of witches as a class. The Complete Book of Necromancers has a confident voice and deploys genre tropes with precision.
Overall, I think this book is kind of wasted on DMs. You can use it to create some memorable villains and settings, but if the players as a group bought into its aesthetics and priorities, you could really elevate your D&D game into something special.
Or maybe I'm just saying that because Talib is a pitch perfect Exalted character - an expert warrior, powerful psychic, and master sorcerer who ruled a city of the undead until he became estranged from his similarly mystical wife and has subsequently spent his later years hunting the most powerful liches in the world.
The best parts of this book are little things like that. Well-chosen details that suggest whole worlds just out of sight. There's an "Anatomist" kit that steals liberally from works like Frankenstein. The signature character for this kit is named "Lady Doctor Ellandra Tolbert." In one of the chapter-opening fictions, she wipes out an entire pirate ship with a single spell. "Once the distant screaming abated, the Lady warned us to leave their ship behind, as a warning to others."
It's so damned rare for a book to just get what I find appealing about playing a magic user.
Ukss Contribution: So many good choices. Almost every page in this book has something awesome (even the part about dual-class necromancer/thieves very awesomely cut the bullshit and called thieves a near-useless class).
My first instinct is to add the worshipers of the God of Suffering. I like this one because it's quite clearly riffing on the dourest strains of medieval Christian theology, but is weird and specific enough to maintain plausible deniability. Usually when games do fantasy Christianity for fantasy Europe, they stick with romantic King Arthur-esque paladins. It's a nice change of pace to see itinerant monks wandering the countryside whipping themselves in a constant reminder that life is a vale of tears.
However, every time I see the priests of the Crying God discussed, people seem to get very weird ideas in their heads about BDSM, and that's not something I want to have to deal with.
I'll go with my second choice, then - The necromancer Nebt Bhakau. He has near perfect regeneration, and was only defeated when he was dismembered into six different pieces, each of which had to be contained in a magically sealed vessel. But if the six jars containing his major organs are brought together once more, he will rise again.