I am a huge fan of Whispers in the Dark. This book is a awesome collection of player options for that system, or any other 5e game. the magic system is a wonderful blend of risk/reward and the lack of firebolt and other combat heavy spells is a welcome change in pace. I like that spells are expensive and not guaranteed to work. The occupations are also a great addition. There are a total of 28 now and I know my group will enjoy playing them all.
My only hope is that we will see a core book that includes all of these rules/options at some point. With the quick start rules, this book, Lamp Light Sanitarium, and the soon to be released Chicago campaign - I can imagine new fans of the game struggling to know where all the material is.