Probably the best part of it, in my eyes, is the description of a needed revision in explanations of Quantum Field Theory. True, the descriptions used in current textbooks rely too much on the historical, today quite antiquated, ways to explain the content of the theory.
Apart from this, Gell-Mann gives an interesting wide view of the simple and complex in nature, from his perspective of an amateur ecologist.
For readers of popular science books the following might be useful: It reads as an intermediate between Richard Dawkins' "Blind Watchmaker" and Anthony Zee's "Fearful symmetry" or Michio Kaku's "Hyperspace", but is less entertaining. It is delivered in a more serious tone of a physicist of an older generation. If it serves your preference, it is a good read. It is not so geeky as Hofstadter "Goedel, Escher, Bach" or "Artificial Intelligence", and is also less physics-centered than "Emperor's new mind" by Penrose.
The book is from 1994, which is 20 years ago, but Gell-Mann correctly predicted up-rise of social media and political consequences of implosion of Soviet Union and fall of communism. This makes it a surprisingly up-to date book, and a valuable read.