Authentic Thaumaturgy, Second Edition
(To begin with, let me say that I'd read Isaac Bonewits' other pieces for years, and have even met him at a pagan festival I attended. So I'm not entirely unbiased on this.)
Bonewits' book is meant to simulate magic as practiced by those operating within a Western esoteric tradition framework. However, it is not a strict simulation of that tradition - most RPG players want impressive results immediately, not a seemingly-coincidental event a few days or weeks from now. Instead, it builds upon it to create a system that allows for the standards of the fantasy wizard's trade (turning opponents to stone, throwing lightning bolts, and such), while providing elements that those who favor less complex systems.
Bonewits' system of magic builds from a list of various sorts of psychic phenomena (psionics and magic being identical in his scheme). This may seem an unusual approach, but then the author does an admirable job of showing how these may be extrapolated into almost any sort of spell effect, ranging from the traditional to the experimental that give GMs headaches when their players discover them. Also included are a number of anti-psi effects, and a large number of different kinds of shields and fields that can affect a spell cast upon the wizard. Both of these are well worth examining in search of new spell effects, though I worry that they might be so powerful that no one will even think of throwing a magical attack at someone.
The spell system itself is, at its heart, a simple thing. At character creation, the first important element is a character's Psi Potential, which determines the amount of magic they can know. Next, the player rolls (or chooses) their character's starting psi talents or anti-psi powers, which describe their capabilities. The magical strength and power inherent in a character is then determined, as is the maximum percentage chance that the player will succeed in a spell. Converting an existing character to the new system is more difficult, as it involves determining which powers the character already has and transferring them.
When casting a spell, the character attempts to tap into various magical laws to raise their chances (charming a dragon is easier with a dragon bone wand, for instance), and tries to channel more power, or mana, for the effect. The player rolls d100, trying to roll under a percentage, and if successful spends the required amount of magic power to accomplish the effect. You might think of it as a less pretentious Mage a la Chaosium's Basic Role-Playing System (though AT pre-dates the first game and was originally commissioned for Chaosium).
Then come the chapter for determining power and success, arguably the book's weakest point. This section contains many equations, often based on laws of physics, for accomplishing the magician's ends. This is probably the most mathematically complex system I've seen in a role-playing game, and it would have you reaching for a calculator every time you want to determine a spell's effects or duration. If you're smart enough to understand these equations, though, you're smart enough to decide on your own spell costs.
I'd suggest skimming over this part and going to the theory parts of the book, where Bonewits shines. What are the basic laws of magic? Why does it work the way it does? Who should be allowed to perform it? What factors make a spell to succeed, and which cause failure? Bonewits presents full yet easily understood answers to all of these. Next comes a discussion of magical items (greatly toned-down from their AD&D versions) and magical beings (greatly enhanced). All of these topics are approached with logic and not a little humor.
The book goes on to discuss clerics, who are simply magicians who can tap into their god for extra powers. The basic point of this section is one that will be familiar to many veteran players, but the explanation is clearer than any other I have seen. As a side note, Bonewits cautions GMs not to use real-life deities in their games, as this might allow them to tap into energies created by collective thought that gamers are not prepared to handle. I am not entirely certain why this should not also apply to concepts such as dragons or aliens, but it might explain why few gamers of my acquaintance have normal lives.
Bonewits runs out the book with his "The Quest for the Sacred Mehleetah", the tale of a sacred quest undertaken by the priests of Caffeina. Very few groups of my experience would play this without copious quantities of alcohol, but it's fun and serves as a good example of the system in action.
One item on which I disagree with Bonewits' approach is his lessening of power for "part-time" spellcasters. If we examine case histories of magicians in different cultures, most magicians are part-time, taking up their duties whenever needed and spending the rest of their time as farmers, artisans, or whatever. This is probably instituted for game balance, but I wish a more elegant way to handle it had been included.
I should note Mr. Bonewits is one of the founders of the Neo-Druid movement, and has strong religious views that he is not shy about expressing. This might turn off some readers, but it's refreshing for someone to be so forthright rather than concealing their views behind the game's mechanics or source material.
As to presentation, most of the art is done in imitation of old woodcuts. If you like that sort of thing (as I do), you'll appreciate it, though others may find it too angular. Along the top and bottom of each page are curious characters which, according to Bonewits, spell out messages. I tried to decipher them, but failed utterly. If nothing else, though, they are aesthetically pleasing (though I'd caution him to watch for those null characters that turn up as circles). Overall, the book's look is decent, but not stunning.
My high rating for the book should not suggest it's for those who are content with their RPG magic systems, or who want something they can plug into their games straight off the page. However, if you like to tinker with your magical system, if you run a campaign in which wizards play a major role, or if you want to read a book that has influenced countless game designers since its first publication, this is an excellent addition to your library. You may not use all of it, but borrowing even a few elements should add to the richness of your game.
Style: 4 (Classy and well done)