Lets talk about our opinions about this book.
Mine can be summed up as... Realms of Terrinoth is a very beautiful, high quality tease with incredible expansion potential.
It has so much art that takes up so much page space that FFG could have easily added in a lot more actual game content but decided to use this book as a display of its many beautiful art pieces. This is especially true of Chapter One and while Chapter Two adds a bit of new game stuff for us... Heroic Abilities, new Races, new Talents, Alchemy and the Runes are all good but... They totally chimped out on expanding on the core Magic Skills rules in the Genesys core book. Like, this could have been so much better.
Chapter 3 is incredible. Lots of world fluff (I want more of it) and super cool bestiary with a lot of different flavor. But even here the amount of fluff isn't a whole lot. Just enough to get started, but could easily be expanded into its own 250 page book.