Pretty much everything about this book is spectacular and amazing, so ill try to condense my thoughts and give you a list of what I loved in this and what I didn't.
PROS: 1. Quality- The hardcover book feels like its well made and will last through many years and many campaigns, the pages feel like high quality magazine pages. 2. Content- It has great descriptions on hundreds of creatures and monsters. The vast variety is the main selling point here and it does not disappoint. 3. Quantity- The number of monsters and just thinking about all of the work that went into making them is mind boggling. There are stats for everything from bears to humans to dragons and descriptions on everything as well. So many things you will never run out of ideas for an encounter. 4. Freedom- The biggest thing about DnD that they say over and over again in these core books is that the choice of what to do with everything they give you is yours. You dont have to say that zombies come from necromancers, you can say they are virus zombies that multiply like fungi somehow and make 20 different versions of the zombies with different stats based on the template they give you as a starting point. Thats the beauty of the system. Freedom of choice. 5. Artwork- The art is absolutely beautiful and well done. It looks like watercolor and is nicely detailed. The creatures are shown to be just as amazing as you would imagine them to be.
CONS: 1. Weakened Tarrasque - Some wierd choice by the writers made the Tarrasque not as immortal as before.