The Kobold Guide to Worldbuilding is a very good and useful book. It contains essays written by the top professionals of the tabletop gaming industry, and it does deliver on it's promise, which is to help you make your own world. But I think that the book could benefit from a bit deeper insight on many of the topics, although some (religion, for example) are already excellently covered. Also the first essay makes it look like a detailed history for your world is unnecessary, but the later essays seem to contradict this. All in all, a good book, and I recommend it to all who are currently in the process of worldbuilding, or soon will be.