I'd not posted my thoughts on this part of the Alpha yet, despite having gone through it with a fine-toothed comb and testing it next to some of my own creations using the 3.5 MM. I was moved to post a (brief version of) my notes after reading the same section in the 4th Edition DMG - it's handled infinitely better in the Pathfinder Alpha.
Making monsters is largely an art over a science and lots of different things that you cannot anticipate in a rules system will have an effect on the end result. E.g. A fully 'optimized' party (oh lord, do I hate that phrase) will probably go through monsters a lot quicker and of a higher CR. You can't have two CRs, one for flowery thespians and one for die hard munchkins....
That said, some sort of rules system or guide to working within the main rules (i.e. 3.X) is necessary. At the very least it would need to be a part of a 'designers kit' handed to companies who publish compatible rules material. There are some 'gray areas', but this is necessary because the section is a guide and not hard and fast rules. Whilst these guides can be stuck to as immovable rules, it leads to some strange results, which is why 1) it's a guide and 2) it's at least as much an art as it is a science.
Some sections of this guide will always be arbitrary. E.g. Not all monsters that are bigger in size are going to be necessarily tougher. But at least this is an arbitrary assumption that holds true for both common experience (a 60' monkey is going to be harder to kill than 6' monkey) and the majority of monsters (a hobgoblin is a big goblin and tougher to kill).
The Pathfinder system is great, it provides ball-park set figures for the most important measures of the creature. Whilst, as a DM, I'm more interested in what the monster is doing in the game, it can't do it's job in the game if it's stat-block doesn't cover everything it needs to. Thus, the stats, as a reflection of the role the creature is to play in the coming battle with the PCs, are the most important part of the monster.
The Pathfinder monster creation guide gives a choice of values and lets the creator plot the monster on a 'bare bones graph' which gives all the essential stats e.g. AC, HP, Saves, Save DCs, along with the corresponding expected ranges. This is the clever bit because you can check you are hitting these values after you have finished your creation. After you have added special attacks, reduced some stats in favor in of others etc. you can come back to these values and see if you are right. You can even manipulate these values like the other aspects of the creature, creating a range that is easy to apply to the PCs and their ACs, HPs, Saves etc. and see how it fares immediately.
I've compared some monsters I worked out before the Alpha with a copy of that same creature, made with the Alpha guide. It's very easy to use the guide and the results complimented each other perfectly. That is to say, that the monsters that proved slightly too tough came out at higher CR and those that were easily defeated by the PCs came out at a lower DC. Although I have to admit that I only looked at Aberration, Fey, Giant and Undead and all within the 5HD-16HD range.
I should also admit that I've not looked at the monster conversion section as I've had no problem converting any 3rd edition product to the 3P rules.
Well done! I'm looking forward to using the guide again soon, when preparing for our next game session.
Peace,
tfad