I'm actually in favor of the idea of the book; I like the idea of a book that shows a GM how to portray great evil in such a way that it throws the good deeds of the players into sharp relief. But I feared that it would give typical D&D treatment and reduce everything to flavorless mechanics, i.e., "He does 2d6 damage instead of 1d10, because he's eeeevil." Such things do little to strike dread into my heart.
The book is not completely free of that sort of thing, admittedly (for example, hard-to-heal vile damage seems to me like a nuisance instead of a heart-chilling effect), but it usually rises above it. Had I realized it was by Monte Cook, I might have been more optimistic about it, for it does bring in some of the traits I liked about Arcana Unearthed:
- Lots of flavor. I've noticed this particularly in the spells section that I've just been reading, where almost all the spells are appropriately creepy. The first example that comes to mind is spider hand, which turns one of the caster's hands into a monstrous spider that can act independently.
- Flexible mechanics. For example, there are some nefarious magic components that can be used to enhance any evil spell. That's a nice versatility. (Though there's some wonkiness on the pricing of those components, though--a large dragon's heart should cost much more than the feather of an intelligent flying creature, but as it is, the dragon's heart costs 7gp and the feather costs 20gp.)
- Smoother transitions in mechanics. For example, many of the spells aren't all-or-nothing based on a single saving throw; you get multiple saving throws to throw off some dire effects, or they have a lessened effect if the save is made. The mechanics for sacrifice leave you very likely to get some boon, even though the quality of the boon depends on the roll.
- Genre emulation. I see some efforts to avoid some of D&D's wonkinesses. For example, corrupt spells involve some sort of ability drain--so there's a good reason not to pump them out every day.
There are some ideas that would fit well into my campaign's themes. In particular, some of the prestige classes would fit well... but I'm not sure where to fit more nefarious NPCs into the adventures I have sketched out. Must think on that.