I personally like monster products that give more then a list of stats. Undead of Ados is an axcellent example of a detailed monster manual. Each entity is covered in 3+ pages. After reading the entry, you will have the exact niche the creature will fill in your campaign. You will also have answers for almost all questions your players come up with, from ecology to monster lore checks. There are enough suprises for each creature and the mechanics are solid. In short this is the type of product that other companies should look up to.
The only shortcoming is, I was expecting monster icons of each creature, like those in the Brixbrix's Field Guide to the Creatures of Ados. I can make my own from the well drawn pictures of each entry, but still one looks for perfection :)