This book is amazing, simply for the fact that it really allows you to understand the major layers of a computer system in a way that can fit in your mind all at once. This is not an easy task, with each layer having the capability of being a highly specialized area of study. You can spend your life working in operating systems without ever really understanding what a compiler does, or work in compilers without ever actually understanding the digital logic that underlies computer architecture.
For students and hobbyists alike, the task of understanding what a computer fundamentally does can seem like a truly uphill battle. Approaching this battle from the top down can seem never ending. The number and complexity of layers between application code and executable binaries is daunting to the newcomer to say the least. Approaching it from the bottom up is still difficult, but it allows you to see the need for each abstraction layer as the shortcomings of a lower layer present themselves.
This book takes this bottom up approach to literally take you from digital logic to high level software, literally from nand to tetris. And while each layer in between is highly simplified, it allows you to understand a system as a whole rather than concentrating on the specific layers. Really, a great read. And the projects are priceless. If you make it through this book, you will understand how computers _fundamentally_ work.