Please understand, ink and space is limited when a book is put together. Paizo has to choose carefully what they put in as apposed to data overload. As a player, the reason I bought the Bestiary 5 is the monstrous humanoids, humanoids and undead. As a GM, I feel the roles of the Beasties are different and have fire power!.
The polymorph school is fun! I get to turn into monsters! Monstrous humanoids, humanoids and undead are the beasties I can turn into and keep my armor, sword and the like when I turn into them.
Polymorph is like gas on a camp fire in a fight. Getting larger, and for example, having multiple arms creates options. You can carry a reach weapon and a melee weapon to threaten all squares you threaten you can reach. For changing shape to a larger creature, increasing to a size large creature gives a +1 to attack with CMB against CMD unlike a -2 to attack AC. For turning into a size Huge creature, a +2 is given to attack CMD with CMB. There is a size Huge monstrous humanoid with more than two arms in the Bestiary 5. I can only think of one size Huge monstrous Humanoid in all the other Bestiary's.
That means Sunder, Trip, Grapple, Reposition and the like are incredibly successful on low rolls the larger you get. Not to mention the damage output increases along with reach in which creatures smaller than you can not take a free shot if they can not reach you when you provoke. There are lots of reasons to enjoy the book as a player. Monstrous Physique I, II, III, and IV here I come with more ammo!
I like the layout of the book, the stats of the monsters fulfill roles that the other bestiary's do not completely fulfill as in the example given above. As a GM, ever since the first bestiary, the monsters are scarier and scarier as each Bestiary has come out. That means as a player or a GM, the fire power can be increased for the players and more fire power means more epic fights.
As a side note, I feel the story should propel the fights just like it should propel the role-playing, investigating or what not in any adventure. The book propels the fights, but the fights are the most fun of Pathfinder. The rest of the flavor of the game is like mortar around the bricks in a wall. All of it is needed to complete what the purpose of a brick wall or an adventure in relation to the first sentence above in this Paragraph.
I have noticed players like fire power. The more people play the more fire power they would like to have. Such increases means greater rules struggle. The more I play and understand chapter 8 & 9 of the core rule book, the more the rules become easier to use and that struggle has become less. Pathfinder Forever!!!
