5 out of 5 rating for 13th Age Bestiary
I've taken the time to really digest this book. I've read it at least three times from cover to cover and quite a few of the critters have seen me pour over them quite a few times.
The down side for me is the format (font choices, title spacing, "blank" space, etc) : it is ok. But I don't like it.
On the other hand:
1 - all the critters presented have a slew of information that is all potentially useful : adventure ideas, world building ideas, just a fun read, etc, etc. It is impressive.
2 - all the critters have a cool mechanical hook (or three!) and I've not seen one where the mechanics don't "jive" with the fluff. (As a counter example, the 5e ogre - out of the box, it can't do anything I imagine an ogre should be able to do; i.e. knock people around, throw huge objects, etc. As per the rules as presented, they don't have the tools to do any of that satisfactorily...)
3 - the art is slightly "toonish" (not in a silly way), and it also works well to show the critters. If "toonish" art is not for you, you might not like it, but the quality is there and the representations are excellent. I have another complaint here : the manticore shown is not the "main" manticore, but rather an "optional" variant. It looks really cool, but it's kind of strange to showcase that one...
4 - you get great tie-ins into the default political structure of the 13th Age world. All of it is easy to rework, and having it presented is a font of inspiration.
5 - interesting critter twists. Most "standard" monsters have already been presented, and all those presented here have something new to offer - there is no "plain-Jane" in this book.