Volume 2 Book of Monsters kicks off with a fantastic illustration of a hydra by John Dickson Batten. Love this artwork.
Initially he lets us know that most of the monsters we "have come to know, 'love' or in a few cases merely wonder about" are present. Some of them are given a twists and to me that enhances this book way more than an exact copy would.
He tries to go back to the original conception of Armor Class. I could repeat hear how he defines that, but I won't, you should check it out yourself. Also he says that he rejects the "creeping 'naturalism' of later interpretations" and I completely approve of this approach.
He also ties this in with Volume 1 and the approach to language and religion. I like this a lot.
I enjoyed the way that he "fleshes" out Androids with both description and stats. Also he provides equipment they might possess. I should note here that what he has done in this book should encourage everyone to create (over time, not in one sitting, unless of course you are capable of doing that) your own version of things. Keep things fresh for your players, make your monsters malleable over time and not static.
Apts and other Barsoom critters get stats and descriptions.
Mundane animals also get descriptions and stats, making this a very good introductory versions for newbies. Descriptions are clear and short. Dinosaurs also get stats and description, this game is ready to go. Again don't limit yourself to just the printed page, add your own stuff. Other prehistoric animals are included.
Cyborgs get a similar treatment to that given Androids.
Evil High Priests or Priestessess get a great writeup. Worth reading just for this IMO. Along with Evil Lords and other Evil Men (such as Evil Magic-Users). Evil (not High) Priests are included too. Great section to help a beginner who might not know where to start.
A number of normal insects are provided, some harmless, but with side effects to the PCs in interesting ways.
Some gods and goddesses are provided, he did look at all the supplements.
Golems are also "fleshed" out in interesting ways.
A writeup on half-elves should prove useful to the many who like to run half-elves in their game. I think his take on them should be fun for all in a campaign.
I could keep going and go into more detail as well, but I will not except to encourage you to check it out, this is well done.
Here ends my comments on book 2.