Short and sweet: this book is about structuring and analyzing problems, not about solutions. In fact, from the beginning the author discusses the difficulty of focusing on problems and the tendency to jump to a solution before the problem is completely understood.
The structured approach that Mr. Jackson provides starts with bounding the problem and drilling down into subproblems, called problem frames. I like his approach to bounding problems because it shows how to identify and isolate the problem and place it into its proper context. This forces you to focus on the problem and not drift off into a premature solution. I also like how he breaks down problems into manageable chunks by placing subproblems into domains through the use of projections (where subproblem domains overlap) and partitions (where associated phenomena are isolated). This allows you to see the whole problem in its magnificent splendor, which is the first step towards tackling each of its parts.
As Mr. Jackson's approach evolves you will find patterns emerging. If you are a proponent of design patterns you will appreciate how he breaks problems into classes and five basic frames. This is a powerful concept because as you gain experience using problem frames you will be able to quickly classify problems and approach them in a consistent, repeatable manner. This part of the book greatly influenced my way of thinking about problems, and the material is reinforced by examples given in subsequent chapters, as well as chapters devoted to variant and composite frames.
This book is ostensibly about problem frames and methods as they relate to software development. However, the approach given in the book has much wider applications. I was able to relate it to physical devices, processes and procedures. Moreover, Mr. Jackson's approach itself can be decomposed into a collection of useful tools and techniques that, taken individually, will prove invaluable in requirements analysis, design and related endeavors. I am giving it 5 stars only because I cannot give it more.