Filled with an interesting take on magic in comic-style settings, Green Ronin's Book of Magic is a useful addition to any campaign that incorporates mystic elements an uses the M&M rule set. While not essential for any such campaign, it's a great guide on how to incorporate the feel of comic book magic into any setting. The Freedom City examples, while specific to that setting, are a fairly comprehensive example of everything the book discusses.
For those looking for Freedom-specific information, there are a wealth of new threats, allies, informants, organizations, and a deeper exploration of the mystical history of that setting.
What it is: As the introduction does a very good job of explaining, this is a book about magic as it works in comics. It doesn't explore the nearly limitless types of magic covered in various fantasy settings, the variations explored by real world mythologies (past and present), and only touches on the magic as mind-destroying horror in the briefest of ways. Instead, magic is treated as a mysterious, complicated, and slightly dangerous (because of the attentions it draws, rather than the nature of magic) source of power and stories. While not as comprehensible as super science, it is still understandable and generally follows a set patter.
The Layout: The book is split into four chapters.
The first is about the mystic world, and focuses on tone, stories, and fundamental concepts found in comic book magic. There is a fairly significant analysis of the progression of magic in the histories of both DC and Marvel comics, giving some good insights into how magic in comics has evolved over the decades. It has long sections discussing the complex role play and characterization aspects of being steeped in magic, as well as providing guidelines on the various mystical dimensions that exist in many settings (and the powerful denizens thereof).
The second chapter is for mystic hero creation, and includes both suggestions to build the desired character and a few new options (feat uses and power flaws) to make the magic work the way you want it to. It also includes a library of 'common' spells in the Freedom City campaign, their origins and associations; this information is useful for both spell building and setting enhancement, providing examples useful to any setting.
The third chapter is all about mystical campaigns (series in M&M speak). The long lists of villainous archetypes, supporting characters, and a short section on frameworks for a mystic series are all found here.
The fourth and final chapter is an exploration of magical characters, locations, history and ideas in the Freedom City setting. While the entire book is useful for any mystic series, this chapter is most useful either as examples / inspirations or for GMs running a series set in Freedom City.
Wonderful advice on mystic campaigns. This stuff is golden, even for settings with completely different limitations and concepts of magic.
Templates. I, personally, really like templates for beings of roughly the same type, and this book has a wide variety of them, from Olympian gods to Asgardian dwellers to angels to fey to hungry dead to demons galore. Enough templates to keep me happily building nasty NPCs for months.
The character concepts. NPCs, PC ideas, villains, whatever, these concepts are interesting, deep, and well thought out (though not all their mechanics are). Even the villain archetypes, though they draw upon pre-existing ideas, are great inspiration and have some fun twists buried in them.
As so often happens with Green Ronin products, my principle complaints are with the NPCs. The concepts behind them are often brilliant but many of the builds lack mechanical refinement. And the supporting archetypes are almost all flawed, with incorrect PLs (Fire Giant's fire aura; Academic, Antiquarian, and Humble Servant, given their skills), poorly added abilities (Minotaur's damage with his strike), feats used incorrectly (Mage Slayer's favored opponent should add to his damage, not his attack), or poorly chosen abilities for the concept (Nightmare Rider powers, or the Iron Golem's mental ability scores given the flavor text). Still, this is only really a problem for Game Masters that pull things out of the book without examining and modifying them first. Or people reading the entries to try and better understand the rule mechanics.
A minor complaint is that some of the Freedom City NPCs are repeated from other sources. This is especially minor since they are completely appropriate to the book and this keeps the reader from having to flip between multiple sources to see what they can do and how well they can do it.
Overall: A great book, but specialized.
If you're using some, or many, mystic elements in your M&M series then this is probably worth every penny.
If you're not too invested in magic, or don't want to be, then this isn't so good. Still worth picking up, if you can find it on sale (at $10 or less this book is worth it even if you don't run a mystical game), but probably not quite worth the list cost for those not running mystic-heavy campaigns.
I've enjoyed reading it and have picked up a bunch of fun inspirations, villain ideas, complications, and plots to plague my players.
Scoring: I held off on that last star due to the specialized nature of this product and the fact that it needs someone to go over all the stat blocks and make sure they fit their PLs (or change PL to fit their abilities). With corrections it would easily be 4.5 of 5 and I'd be sorely tempted to round up.