This book is absolutely incredible and as a GM, I cannot wait to be able to keep using this supplement.
Firstly, the amount of work that has gone into this is commendable, there is an extensive list of monsters with plenty of variants and all of them have been spectacularly made. From the few monsters I've been able to throw at my party, all of them are very nicely balanced and I'm certain I'll continue to find that as I keep using monsters from here.
Another thing I want to point out is how useful this is. I'm sure everyone's been in the position of wanting to use a certain monster but not being able to because the players are either too weak or two strong. If you've felt that, this module is a god(s) send because of the high and low level options it has for established monsters, all without feeling like your players are losing any of the experience.
It's definetly a 5/5 from me because of the versatility and level of quality within. Absolute must have for any GM to get themselves (or players, a great gift to your GM). Not to mention the formatting and layout of the actual pdf is really nice and well done.
All around a great product!
[5 of 5 Stars!]