The purpose of this book is a deep-dive into API design for developing complex frameworks on the .NET Platform. There is a lot of content on developing 'good' APIs and usable architectures for clients of the frameworks. This book is entirely .NET Framework focused, so it will probably only be of use to those with a passing knowledge of this and C# in general (examples are in C#).
With this caveat out of the way - the main reason for my recommendation is the wealth of anecdotes and side-bars from some of the well-known architects / associates who designed the .NET Framework. These take up a reasonable amount of the book, discussing reasoning why the .NET Framework and associated technologies are designed the way they are, the design trade-offs that were involved, and which of their design decisions they would change in retrospect. Often, the authors of these side-bars disagree with each other as to the right approach, further highlighting how much 'art' is involved in this process.
This sort of frank discussion on design, architecture and the consequences of the decisions you make over time is something I haven't seen in many other technical books. If you have any interest in this area, and the exposure to the technologies involved, this is worth a read.