You can buy this in PDF version on the Paizo website. Dont. This book is an awesome piece of art, full colour with really coherent artistic style. As a GM I flick to the monster and show the PC's the pictures therin, and watch them assimilate it in to their mental movies.
I remember when my group first encountered a horde of Dark Creeepers and whilst they were going "what the hell", the tall and powerful dark stalkers appeared. from just looking at the pictures they knew they were in trouble.
And the ecology sections and special attacks are super clear.
As a player you can look at some of the creatures and build your whole theme around them. A paladin emulating archons or angels, a summoner with infernal themed monsters and eidolon.
if you are playing pathfinder, you need this book and the core book at very minimum. Stop reading this and buy the bestiary.
its like a fully vorpal book of awesomeness, a plus +5 to you game immersion roll the next time you play.