Ed Greenwood has a way of suckering people into buying his books, no matter how useless the material. Though prolific, he rarely writes anything of value, or which displays even one iota of creativity. Secrets of the Magister is little different.
Though this sourcebook is not riddled with impossibly-high statistics of godlike characters, it follows the Greenwood mold. In his quest to create a thorough, detailed world, Greenwood has introduced a plethora of facts, from the trite to the trivial. Secrets of the Magister takes an otherwise mysterious being and, by revealing its secrets, not only brings that lofty title down to the mundane, but drags it through the filth of artificiality.
None of what Greenwood writes feels real! Granted, it's a fantasy world, but if we are to suspend disbelief, as is the goal of role-playing, then the magical should seem wondrous, not mundane; characters should feel alive, not artificial; and adventure should be high and fantastic, not removed and routine.
Half the book is devoted to a brief history of the magisters, which is as dry and didactic as a textbook. A good portion deals with special spells and magical items employed or created by magisters past and present. This is of some value if you want some new spells or magical items to introduce to a campaign and are not feeling particularly creative at the moment, but it is such a small, unoriginal sample that this books is not worth buying just as a magic supplement. Finally, Greenwood deals with the attributes of magisters, how they are selected, what benefits they receive, etc., all with the enthusiasm of a lich in a dead-magic zone.
Browse through the book if you want, take a look at the spells and items, but don't bother buying it...chances are, you'll come up with much more creative and superior material on your own.