There are lots of books which help you get the job that you want, but there are very few that help you figure out what you want in the first place.
This book has guided several people that I know through their midlife crisis by helping them identify what sort of a job they would find more satisfying than whatever it is they are currently doing.
The structured exercises force you to examine every aspect of your life including what you enjoy, what you're good at, what you spend your time on etc. If you put in the time and effort you will end up with both a reasonable idea of what you want and some idea of how to get it.