There's a lot to say about this book, some of it good, some of it bad. For the most part, I can say that it is a fun book with a lot of interesting archetypes and character ideas, along with a few good feats, cool spells, and thoughtful mechanics. Of course, the exact same points could be made against the book: useless archetypes, pointless feats, silly spells, and bad mechanics.
Ultimate Magic suffers the same problem a lot of supplemental material in 3.5 did, in which the book does not feel as tight design-wise as it otherwise could be, given the incredibly limited application of some of it's contents. Consider the Witch hex "child scent," for example: When are you ever going to need to sniff out children? This feels like a villain-only ability, and even then you could probably give your villain witch a more useful hex. The same goes for the construct modifications. They're neat, but they're not worth it to most spell casters, better used for a dramatic villain fight than an actual player. Or maybe "cartoony" would be a more appropriate description- there's something strikingly reminiscent of Power Rangers that involves the bad guy combining with his robot helper. Also: The geisha Bard archetype. What the heck, man. Tea ceremony, really? It's neat and flavorful, but it breaks flow and forces me as both a player and a GM into that uncanny valley of "yes, I suppose you guys do technically have 10 minutes outside the boss room." I mean, it's not like the dragon's going to eat the princess any time soon, or anything...
Of course, for all the bad ideas there are good ones too. The magus looks like a fun class, albeit he loses out on damage output against classes such as the barbarian or the rogue, but he makes up for it with the versatility of spellcasting (and I absolutely adore the staff magus archetype). I also really like the customization of the Qinggong monk, and think the alternative channeling powers are amazing. However, these traits alone to not make the book great, only good.
Also, this is a nit-pick, but Paizo didn't fix the typo in the vivisectionist archetype for the alchemist. This typo was pointed out when they previewed the archetype, the editors responded to the post, and the mistake still made it into the final printing. Vivisectionists can't benefit from plague bomb because they don't *get* bombs. You think that a company as good as Paizo wouldn't let a mistake like that slip past them after it was brought to their attention.
In conclusion, Ultimate Magic is one of those books which is handy to have around for the additional options, but is by no means a "must buy."
