As most people might already know, this book is based upon the Christian movie "Fireproof", which is about a man who saves his marriage by completing a character-testing, 40-day list of "dares" suggested to him by his father. Like the movie, the book of course is Christian based as well.
I loved the movie and the book is more of the same. However I looked at both of them from the perspective of a person happily married for over 15 years. I can tell you that while I don't practice all the dares in the book, my spouse and I are good about doing many of them- and of course there's always room for improvement. From my personal experience, I feel like concentrating on the kinds of ideas presented in the book have been absolutely key to making our marriage last.
Now the book itself also consists of a 40-day list of dares. For each day, there's about a page and a half or so of advice, followed by a specific dare and some space for you to write down your personal reflections. Dares range from things such as practicing patience to writing out a renewal of your vows. The guys will probably particularly like Day 32!
As you can tell, I highly recommend going to see the movie and reading the book. In a society that places a high value on looks and money, while sporting a 50% divorce rate, its nice to see more movies and books coming out that get people more focused on the right values in life. Even if you don't do anything more than just glance through the book, you're going to be given something to think about. Other self-help books I enjoyed include "Finding Happiness in a Frustrating World