Let's get this out of the way first - I really like and enjoy both the book and the principles behind it. The idea of a general system theory (GST), which transcends the mechanistic worldview and moves more towards an organistic one, where bits are not broken down for individual analysis only but where a synthesis is attempted as well, and where a holistic view needs to be taken for a comprehensive understanding of a system are all beyod reproach.
The author shows examples of some general systemic principles, which apply in vastly different fields of science, and which while similar in principle, were derived largely independently. These should form the basis of GST as a discipline.
On top of that, the book has several other endearing and interesting characteristics. Von Bertalanffy was certainly aware off and mentions Kuhn's ideas quite a bit. A specific element to be found throughout the book shows how painfully aware the author is of the implications of Kuhn's work - basically that if a theory does not hit the Zeitgeist, it will vanish irrespective of its superior explanatory power, or at best languish somewhere out of the limelight. Namely the author is quite aware that the mechanistic view of things still holds sway (at the time of writing, and to a large extent 4 decades later as well) over Anglosaxon thought and in the related academic circles. At the time of writing there still was a very strong Germanic tradition, much more suited to the GST approach, which he tries to bind more closely (almost all the concepts he presents, he uses German words for, in order to cement the link). With time this tradition weakened somewhat and this was also reflected in the popularity of the theory.
The other problem is that of the writings being too complex and requiring too much background knowledge, education and thinking capacity to still be popular in the more modern, one minute manager type of world.
It is in many ways still a relevant guide of how to reform both science, our knowledge systems and ways of making decisions more broadly, however I think that it is now even further at the fringe than it was at the time von Bertalanffy first postulated it.
On a practical note, a criticism I find is the relative doggedness one needs to bring to reading it - even though the author had spent several decades living and working in Canada when this was written, the same overcomplex Germanic writing style is used, which in many ways unduly limited the readership the ideas finally managed to spread to. In hindsight some of the areas developed in very different directions from those the author deemed necessary or most promising as well (gestalt psychology), making some aspects of the book a bit dated, when it is read now.
Irrespective of that, I think it is a highly valuable contribution to the intellectual fabric of the 20th century and I highly recommend it for anyone interested in cybernetics, holistic thinking, systemic thinking, system dynamics or control theory.