After the resounding success of Imperial Mysteries, this book helps to bring focus back on the main driving focuses of the game; the personal struggles against madness and mystery as mages seek to advance their own causes and desires in competition with their peers and conflict with their enemies, and the temptations that beset them therein. To that point, Left-Hand Path successfully presents its dark and strange magics as things to draw and repulse characters in equal measure, while also driving prejudices and rationalizations within mage society.
The Introduction gets off to a good start by carefully going into the terminologies surrounding Left-Handed magic, the basic drives of why mages pursue it, and the views of other mages surrounding it, integral tools for creating properly evocative setting and characters in a chronicle incorporating it either for players or antagonists. Advice for how Left-Handed mages can be utilised by Storytellers for various kinds of play experience are also included.
Chapter One focuses on heresies within the actual Orders themselves, as well as those mages who reject or fall away from Order affiliation. It does well for describing dark practices in terms of modifications within the strange philosophies of the Orders, and how they might proliferate and survive, and helps fill out notions of the taboos and traditions that would drive mage society. By presenting apostasy as a matter of irreconcilable difference with the Orders (even after having joined one), it helps to add some depth to them in terms of being potentially problematic. Some nice Flaws are given to help add flavour to these character types. Of particular note is presenting a concept of Nameless Orders, widespread alliances of apostate mages with their own particular minor benefits for joining, something that should be interesting to people who were always disinterested in the presentation or nature of existing Orders.
The chapter also helps reconcile a few previously disparate bits of the Mage cosmology, while also filling them out in a way to make their attraction to mages feel sensible.
Chapter Two codifies the Mad, now defined as mages who, having committed some particularly severe atrocity, have their souls break in a manner that causes magic to leak from them, warping the world in a manner informed by how they broke. The Mad are made quite disturbing as irrational antagonists who are potentially capable of things outside of the usual system, and represent a disturbing end point for particularly driven characters. The systems given for the Mad are highly detailed and interesting, allowing one to tailor such mages to the specific needs of a game or character type, and some specific Storyteller advice is given to help the depiction of this particularly idiosyncratic form of Left-Handed mage.
Chapter Three fleshes out the Scelesti, adding an extensive set of their own mythologies, motivations, philosophies and culture (including recruitment methods and forms of social terminology and organisation). Abyssal forms of magic are redetailed from Tome of the Mysteries, albeit cleaned up a bit, contextualised in terms of Scelesti perspective (and hierarchy), and added to a bit (particularly in the form of a new pinnacle based around the power to deliberately harness Paradox). Scelesti Legacy formation is given new systems for development and joining, and Scelesti cults are incorporated according to the Nameless Order system. Overall, it does a good job of making the Scelesti seem like an appropriately horrifying but understandable group.
Chapter Four covers Reapers, mages who manipulate souls for power. This begins with a useful errata for the effects of soullessness on mages, in order to allow those whose souls have been tampered with to still have a part in the game. Most particularly, the chapter massively fleshes out the Tremere, giving them an elaborate history, mythology, social organisation (highly distinct from that of apostates and Scelesti), and driving and highly distinct philosophical goal. The apparent contradictions of the Tremere state are "resolved" (if only be adding more mysteries), and a number of systems are given to make the Tremere path more attractive (most notably the capacity to essentially steal Legacies). Overall, the Tremere are remade as an intriguing and complex antagonist for regular Mage games. To round the chapter out, two Reaper Legacies are given for the Pentacle Orders.
Overall, the book does quite well to detail the ideas behind stories involving Left-Handed magic, not just in terms of what it can do and why and how mages might be driven towards it, but in the greater context of the Mage setting. For those who wish for a greater variety of Mage antagonists, different story options, and new temptations or questions for players, or to overall inject some humanised horror into their games, the book is a must have.