The Bestiary is 240 a page hard cover with a gorgeous cover painting by Pasqual Quidalt (see Runequest 6 for more of his awesome covers) of an ogre mage woman (I think) acting very threatening to a dragon and some goblins who are all looking out toward the viewer with a look that suggests, "back off, we've got this," all while an ominous structure lurks in the background over a mountainous expanse. The interior art is great, too. It's a more comic-like look (stark lines and color, not "realistic" in the literal sense but very clear and evocative) by Rich Longmore. For example, a couatl:
The book itself is slick, heavy paper and full color: so beautiful book, got that out of the way.
The interior consists of an expository chapter with a breakdown of monster types by useful behaviors (i.e. monsters more likely to talk to you, monsters more likely to kidnap people, etc.) and 52 monster entries, each providing extensive detail on a monster, or more accurately a cluster of monsters that have relationships, be they cultural, physical, or the just occupy the same ugly zone in the 13th Age. The monster entries are a great read, and provide a wealth of ideas on how to use each creature in play, with story and plot ideas liberally strewn everywhere beside a vast array of much needed stat blocks. Sections on icons and how they care (or don't) about the creatures can be found as well.
The book ends with an index on how to re-skin monsters and take basic stat blocks and spruce them up, along with an index of all monsters in both this book and the core rules. It shows how you can take a drider and wolves to create flaming winged fire-poo flinging monkeys (yes, they went there) and how to fancy up a generic wizard using the basic rules guidelines. 13th Age is ridiculously easy to construct monster stats on the fly, but these rules offer up extra insight on how to make your ad hoc encounters just a bit more classy.
So who's in this book? Here's a listing by entry, followed by the specific subtypes therein:
Basilisk - we get a classic basilisk, though the text hints at other more exotic colors.
Bats - swarms, dire bats, bat cavalry (for when you really gotta fly), goblin bat mages, thunder bats, wraith bats....all bats all the time!
Black Dragons - various distinct types including catacomb, gorge, void, and empyrean dragons.
Blue Sorcerer - what happens to lizardmen and other draconics who dedicate themselves to the blue (a complex tough lower level fight).
Bugbears - including scouts, schemers, and barbarous bugbears.
Bulette - the legendary plastic toys turned land sharks appear with green, lumberland dirt-fisher, ravenous bumoorah, and deep bulettes.
Cambion Assassins - the half demons get a decent write up with dirk, sickle, katar and hellblade versions.
Centaurs - including the lancers, raiders, rangers, and champions.
Chaos Beasts - chaos glorp, chaos beasts, chaos brutes and the ever loving chaos behemoth provide all the lurking chaos piles you can stomach.
Chimera - the chimera gets a strange treatment with the iconic chimera, which shifts and changes with the nature of the icons. Neat idea.
Chuul - the chuul appear as regular chuul and swarms, as well as massive mutant versions. In 13th Age chuul are cunningly intelligent and they hate all humanoids, turning those they harvest into chuulish slaves.
Couatl - overworld beings that have deep and weird relationships with the icons, coming in flasvors of classic and elder couatl.
Drow - because we can never have enough dark elves floating around, we now get spider-mages, sword maidens, soldiers, spider-sorceresses (yes they seem to worship the copyright-free version of Lolth in 13th Age), drow darkbolts, and cavalry. Spider mounts, Lokris and weaver swarms provide arachnid backup.
Dybbuk - possessing ghosts from beyond including corpse dybbuk, parasitic dybbuk, and ethereal dybbuk.
Elder Beasts - If you were looking to fight hideous elder beings here they are: the umluppuk and hagunemnon provide terrfying high level encounters while warped beasts provide a taste of things to come. Fans of the Far Realm from D&D will like this.
Ettercap - various editions of D&D have tried to make something of the ettercap...here they are primitive arachnoid-like humanoids who worship "She Who Spins in Darkness," with flavors in hunter, acolyte, supplicant, warrior and keeper.
Fungaloid - everyone needs fungus men. Creepers, aerial spores, sporriors, drudges, braincaps, monarchs, elder spores and the fungaloid empress herself provide loads of humanoid fungus fun. Buried here is a playable race: the mycotic twygzog, humanoid sentient fungaloids that are more "human" in their appearance and behavior and can sprout a little fungaloid buddy.
Gelahedron - if you've ever wondered where gelatinous cubes fit into the ecology here it is. Gelatinous tetrahedrons, the gelatinous cube, gelatinous octahedron and gelatinous dodecahedron will leave you eager to try out these enormously complex boss monsters on your pitiful players.
Genies - The iconic genies take a weird twist here, bound to icons and granting wishes when slain, they include djinn and efreet.
Ghouls - lots and lots of ghoulishness here with gravemeats, fleshrippers, licklashes, pusbusters, and ghasts.
Golems - including bronze and marble.
Hags - presented here as rather complex entities, the hag has one entry with loads of specific customization to create various distinct types. Hags, as you might imagine, have a lot of animosity toward icons and the world.
Haunted Skulls - creepy ghost anchors that include watch skulls, slime skulls, jest bones, screaming skulls, flaming skulls, black skulls and the skull of the beast which reminded me of the horned demons at the end of Time Bandits for some reason.
Hellbugs - not quite the beasties from Defiance but close enough, with boombugs, hellwasps, hook scuttlers and swarming maws. I've already killed a hapless paladin with a mass of hook scuttlers a few games back.
Intellect Devourers - hideous brains with legs created by the Wizard King during his descent into madness.
Jorogumo - imagine the chinese Fox Woman tales, in which the tempress lures you through lies and deceit, but she is ultimately a hideous spider in disguise. Includes the spinneret doxy, lethal lothario, binding bride, swarm prince, and the woven.
Kobold - including the grand wizard, skyclaw, engineer, dog rider, bravescale, dungeon shaman, shadow warrior, and dragon soul. Includes a nice discussion on kobold trap making.
Lammasu - another monster which is often neglected in D&D, the lammasu stands out here in flavors of warrior , wizard, priest and fallen.
Lich - hard not to imagine more on this one here, with the baroness, count and prince versions.
Manticores - includes the dubious singer in the form of the manticore bard, the extra tough mantikumhar, and the stealthy flying coursing manticore.
Naga - loads of various types including swaysong, sparkscale, manafang, and elder versions of all three.
Ogres - learn more about the ogres of the 13th Age then you thought possible with the ogre penitent, demonic ogre, berserker, crusader, champion and minion.
Ogre Mages - left as mysterious super baddies, the ogre mages come in flavors of knights, lightning mages, and prismatic ogre mages.
Orcs - the default 13th Age orcs pull themselves up from the muck of creation and are nasty, brutish and short-lived. We get additional orc types including pit-spawn, archers, cave orcs, death plague orcs, battle screamers, and tuskers, with additional rules on disease carrying orcs.
Predatory Plants - ubiquitous in all D&D style games, we get a menagerie here including claw flowers, pixie pods, and podlings.
Purple Worms - I used one as a sort of "environmental trap" early on in my first 13th Age campaign, could have used this one sooner! Includes the classic purple worm along with the parasitic lightning beetle,, purple larva, and ancient purple worms.
Red Dragons - including flavors of volcano dragon, hoardsong dragon, hoard spirit, greathoard elder, flamewreathed dragon, and smoke minions.
Redcap - sort of like Pathfinder goblins in "Saw" mode. Include the splotchcap, redcap, crimsoncap and crustycap.
Remorhaz - eating adventurers since the 1920's we get the squib swarm, barbellite, frost-wurm, adult remorhaz and queen remorhaz.
Rust Monster - including classic and "obliterator" the rust monster gets lots of fun treatment here as the monster which everyone loves to hate. If you remember the 4E rust monster and its weird "don't take the toys from the players" approach, you'll like this one, which basically rusts your armor and weapons away in a hit or two.
Sahuagin - these undersea guys get around. Here we get stats for the raider, razor shark, classic sahuagin, glow priests, iron sea sharks, and mutants.
Shadow Dragons - our first delve into non chromatic dragonkind with 13th Age, we get the classic shadow dragon, shadow thief, and a discussion on the curses and hexes shadow dragons like to deploy to mess with adventurers...items which include the Deck of Many Cards and Procastination Tome, for example ( 15 new cursed items in all!)
Stirge - classic stirges next to archer stirges (fires barbed stingers), cobbler stirges (hive makers), and stirgelings (babies).
Tarrasque - presented here as one of the few monsters to have slain an icon, a huge level 15th wrecker with 2130 hit points and a huge stat block by 13th Age standards.
The Saved - followers of the Crusader who are dragged back from death to wear haunted armor and gear as they are forced to continue in his service. Includes the avenging orb, destroying sword, and enduring shield.
Warbanner - weird sentient magical telepathic objects, the warbanners get planted and do their damage. Feral warbanners, crusader warbanners, orc lord warbanners, and lich king warbanners all serve the forces of their dire icons.
Wendigo - spirit cannibals brought about as a byproduct of a turf war among icons these include the classic wendigo spirit, ravenous cannibals, and elder wendigo.
Whispering Prophet - a hideous aberration bartering in secrets for power and madness.
White Dragons - We get the hatchlings, cenotaph dragon, mausoleum dragon, blizzard dragon, and moon dragon.
Wibble - accidents of sorcery, these dirty brown bubbles appear to be something to torture the wizard with.
Zorigami - clockwork monsters which are the keepers of time, we get the dawn, apex, and dusk versions.
All told over 52 primary entries and 200 stat blocks, with a ton of scenario and encounter ideas, loot details, icon relations, battle tactics and ecologies. It is a lot, and as monster books go this is one of the best I've read, providing a ton of useful content and doing something I generally feel a lot of RPGs fail at: being an entertaining read as well as a useful sourcebook.
All in all the 13th Age Bestiary is a A+++ product. If you're even remotely into 13th Age you should get it. If you want a great read and don't mind extrapolating from the stat blocks for your preferred edition it might actually be worthwhile, although the Iconic elements of the 13th Age may require some consideration in other games.