This wonderfully clear, simple little book was my first introduction to Systems thirty years ago, and I still recommend it as the best place for a complete beginner to start.
It has been used for everything from executive seminars to graduate programs to high school gifted programs, and it is still the first book in "Roadmaps," MIT's online systems dynamic program for teachers.
I'm not really sure how to rate this book. I had to read it for my doctoral work, so I'm confident that it will be helpful in the near future. In the present, though, I found it boring and very outdated in its graphics and illustrations. The book introduces the reader to the topic of systems thinking with he goal being to help leaders understand their organizations from a systems perspective. Toward this end, it does introduce the reader to systems, though it seems that the next books in he series will be necessary to dig in further. Ask me in a year of this book has changed the way that I read and I'll let you know if it's good or not.