This is an in-depth book covering the generation of local, and national, holidays, to spice up your campaign world. If you follow the directions, and develop holidays for your campaign world, the breadth, and depth, of your imaginary world will expand, dramatically. This product is for those GM's, and players, who really enjoy the role playing aspect of their gaming. If you are into hack-n-slash, move on.
For those who want to make their game world more believable, who want to expand the background of their game world's communities, this book is highly recommended. It covers the why's of holidays, what they are, why they are, and who should celebrate them. It is not aimed at background fluff -- holidays, can be used as springboards for adventures. One example, is that for a particular holiday, a rare herb, or meat, might be necessary. Perhaps an adventure can be designed around acquiring the needed item for the celebration; or, perhaps, all of the needed items for the holiday have been stolen, or maybe even ransomed. The importance of the holiday can be from ho-hum, to critical. It really can be quite useful, if the GM is willing to develop the details, using this book as a guide.
I have been a GM since 1980. I found this book highly useful, and worth my investment, in both time, and money. It is not recommended for beginning GM's. Your experience with this item, and its proposals, may vary. ;-) Cheers!