Inner Sea Magic is a 64-page entry in the Pathfinder Campaign Setting line that contains an impressive amount of information about everything from magical schools to variant types of spellcasting and more. It's full of new spells, archetypes, and even a couple of prestige classes, and I found myself impressed and intrigued by most of the options presented. I will say this is another product that seems to blur the division between the Campaign Setting line (intended for GMs) and the Player's Companion line (intended for players), as players will get as much or more use out of this book as GMs. But in the end that doesn't keep this from being a quality book that is definitely worth getting.
The inside front cover is a map of the Inner Sea region with the location of important magic schools listed. The inside back cover is a reproduction of the cover without any logos or title. The contents are divided into five sections: Magic of the Inner Sea, Variant Magic, Magic Schools, Spellcasters of the Inner Sea, and Spells.
Section 1, Magic of the Inner Sea, is six pages long. It begins with a brief overview (1 paragraph each) of regions in the Inner Sea that are particularly noteworthy in regards to magic: Geb, Irrisen, Jalmeray, the Mana Wastes, Nex, Nidal, Thuvia, Varisia, and the Worldwound. The rest of the section is a list of fifty(!) noted spellcasters in the Inner Sea, each with a one-line description, class and level, and a head-shot. I don't recall seeing anything like this before, but I actually really liked it. It's basically a "Who's Who" of magical power in known Golarion. My only suggestion is that it would have been better to use the inside front and inside back covers for this sort of reference information, thus freeing up a couple of pages in the interior for exposition.
Section 2, Variant Magic, is ten pages long and definitely something I'll make use of. It presents seven variant systems of spellcasting that are tied to a particular region or theme, and are perfect for NPCs or (with GM permission) PCs that hail from that area. Included in this section is False Divine Magic (Razmiran spellcasters who disguise arcane magic as divine), Fleshwarping (not really a different way of casting spells, but a way to transform creatures), Primal Magic (otherwise known as "wild magic", this section includes rules on primal magic areas, how primal magic events are triggered, and a great table on sample effects that could result); Riffle Scrolls (a slightly different method of scroll-casting that I didn't really get the purpose of, either in the novel Prince of Wolves or here); Shadowcasting (drawing from the plane of shadow; this section includes four new feats); Tattoo Magic (favoured by Varisians), and Thassilonian Magic (basically super-specializing in a school of magic; includes a great picture of the Runelord Sorshen). The options presented here were quite flavourful but also seemed (without play-testing) mechanically viable.
Section 3, Magic Schools, is ten pages long and presents a full rules sub-system for handling PCs who enroll at a magical school, including the cost, the benefits (socially and mechanically) they gain from their education, what it takes to avoid flunking out, and so forth. The sub-system is designed to track the students' Fame (which they earn by making Education checks a certain number of times per semester) and Prestige Points (which they earn by completing specific tasks). Fame is used to track a students' progress and privileges (everything from library access at one end to becoming a full professor and receiving a salary at the other) while Prestige Points can be spent to receive specific favors which vary based on the school, such as gaining an Imp Minion or a discount on the purchase of poisons. Formally, the system distinguishes between Academies (arcane education), Guilds (item creation), Monasteries (divine instruction), and Secret Societies (hidden goals). The following schools are detailed, each customized to reflect different entrance fees, tuition costs, exams, extracurricular tasks, and awards: the Acadamae (Korvosa's school of demonic conjuration), the Arcanamirium (Absalom's school of "practical magic"), the Magaambya (a long-standing school in Nantambu in the Mwangi Expanse), the Kintargo Opera House (bardic college in Cheliax), the Oenopion Fleshforges (fleshwarping laboratory in Nex), the Poisoner's Guild (in the River Kingdoms), the White Grotto (a bardic college in Absalom), Citadel Enferac (Hellknight stronghold in Cheliax), the Harrowed Society (Varisian fortune-tellers in Galduria), and the Crimson Citadel (Red Mantis assassins!). Monasteries receive a two-page spread that are not geographically specific, but instead lists a faith-specific award that students can spend prestige points on. Each of the core deities receive one entry. I think the concept of magic schools, and the system presented, would be fantastic fun to use. However, I think it probably would require the entire campaign to be centered around the premise, as otherwise most campaigns don't last long enough (in terms of in-game months) to make a semester structure viable. There is a brief sidebar that suggests a method to cope with this, but I think it could lead to PCs rising from students to Full Professors in the space of what could be only a few months of in-game time, which seems unrealistic. But then, Pathfinder is full of unrealistic things, so that might not be a problem for most. Where I see the Magic Schools sub-system receiving the most value is in a "Harry Potter" style campaign where all the PCs attend the same magic school and compete for fame and prestige while handling missions presented by the school (or foiling threats to the school).
Section 4, Spellcasters of the Inner Sea, is a twenty-page section that tries to offer something for everyone. It's basically a miscellany of everything from new oracle mysteries to new archetypes to new prestige classes. The two new oracle mysteries are Spellscar (centered around primal magic) and Outer Rifts (related to the incursion of the chaotic evil Abyss into the Material Plane). Next, the section lists 19(!) new archetypes. This is already a long review, so I won't list them all here. The ones I've heard a lot about include Crypt Breaker archetype for alchemists (another attack on poor rogues), the Dawnflower Dervish archetype for bards (doubling the benefits of bardic performance, but limiting their application to the bard), and the Winter Witch archetype for witches (pretty much every spellcaster in Irrisen!). Most of the archetypes look pretty good, but there are a couple like Mendevian Priest and Oenopion Researcher that I think could have been fleshed out more. Last, there are two new prestige classes, each with a full two-page spread. The Cyphermage is an expert in written and runic magic from long study of the famous Cyphergate in Riddleport. I really like the flavour of this prestige class, but most of the special abilities apply only to scrolls or other magical writing (like runes or symbols), and, at least in the games I'm involved in, I don't know how useful they would really be. The other prestige class, the Divine Scion, didn't do much for me (apart from a cool picture of Nualia). This divine-focussed prestige class is pretty bland thematically, as it's basically just a super-worshipper of any faith, and the special abilities consist of getting a low-level spell as a spell-like ability and another miscellaneous bonus (tied to the PCs domains), and some other moderate bonuses based on alignment. I think it tries too hard to be available to any faith and just comes across as pretty generic.
Last but not least, is Section 5: Spells. This section starts with a cool picture of the Iconic witch fighting a woolly mammoth with Ice Spears, one of the new spells introduced here. Spellcasters shouldn't be disappointed, as 39 new spells appear here, with at least a couple of options for every spellcasting class (even Alchemist and Summoner). The rich get richer, of course, as Clerics and Wizards/Sorcerors get by far the most new options.
Overall, I quite liked Inner Sea Magic. The sections on Variant Magic and Magic Schools were real highlights, and I could see them adding a lot to the right campaign. The player-focussed options presented (archetypes, spells, etc.) are more the sort of thing that could be found in any book, and I wish that as a Campaign Setting book this one would have spent more time on material that would be unlikely to appear elsewhere. Still, all in all this is a solid buy.