If you like other books by Christopher Alexander, you have to read this set. But, in my opinion I gained so much more from his other books than from the Nature of Order. The goal of the Nature of Order is to explain a new "world-picture" that Alexander formulates in an attempt to transition away from a mechanistic worldview to a worldview where all matter-space and governing physics is a function of animate, spirit-filled "centers" of geometric origin. It is important in this worldview also to view geometry not as static, but as part of a process that extends wholeness of "living structure".
Reading through this, I thought this is quirky and maybe not necessary. And eventually started to suspect things about his worldview that were based on, essentially, animism or pantheism or panentheism. And then, in the last volume, he explicitly states this view as essential to his formula of centers as living beings and fifteen fundamental processes of extending and supporting centers in the overall wholeness of the living structure.
Did I still enjoy reading this book? Kind of. Part of it is very thoughtful and wholesome. His fundamental desire is to create beautiful architecture. The other part is hard to engage with because it either seems absurd or overwrought. Terms are not really defined even though Alexander says they are, and as he advances his arguments and descriptions it is hard to follow because you are either missing the definitions or the terms seem to change their meaning. There is also a lot of confusing language that contains internal contradictions but sounds mystics and so is expecting a pass, like, the universe is connected to the most personal self but in this connection your self becomes the most impersonal in the oneness of the universe (paraphrased).
I am really interested in architecture. I am also really interested in biology, cosmology, physics, theology, and worldviews. So, I liked this set and wanted to read it to the end. But I was also disappointed by the worldview proposed therein. It doesn't reconcile with me as something that is reasonable or true. On the other hand, most modern architecture also doesn't reconcile as reasonable or beautiful, and Alexander's architectural works are beautiful and thoughtful. It is interesting to see the mindset from where his works come from.
If you do not know who Christopher Alexander is, I would recommend not reading these first. I would, in fact, save reading these until you had first read much more by him.