This is a must-have book for Pathfinder fans, and is essentially backwards compatible with 3.X as well. I have so far already integrated the three new player races (saurians, half ogres and ratkin) in to the game, and have seen several of the classes in play as well. The book includes chase rules that look quite fun (haven't tried them yet), a plot path generator, optional character traits, rules on fantasy firearms, and several new classes as well.
PROS: nicely illustrated, well-edited by and large, and it's easy to see that more than half of this book will see play in my campaign over the coming months.
CONS: not much, but mostly that a couple of the new classes are a bit wonky (I'm still scratching my head at the warlock....not a normal class by any stretch!) or boring (cough warlord cough). Beyond that, I haven't encountered anything in this book that wasn't a nice addition to my new ongoing Pathfinder campaign.
[5 of 5 Stars!]