First of all, I must say I love this book. Why? Because of the way how it challenged old Gibbonian Orthodoxy in 1971 and revealed the myth of the “Dark Ages”. This is the way how it should be viewed today: a founding stone of the scholarship of the latest 40 years on Late Antiquity (a term made popular by this work).
The challenge referred above is also the cause of what looks to be an extreme disregard for any kind of decline, yet I think many people attacking Brown’s work fail to have this into account: he mainly seeked to challenge the old decadentist theories, namely regarding cultural and religious History (his specialties), and give an alternative vision of the period between 150-750 AD. That’s the reason of any exaggeration: he was challenging Orthodoxy, not imposing it. However, despite this, I think his work could have been benefited if he worked also with economical History and his approach ends up being limited when it could go a bit further (besides admitting some degree of material/economic decline, in order to turn away most of his critics).
With this said, this work is wonderful. It is read very easily and there are lots of illustrations helping Brown to make his points, yet the ideas he communicates are very deep. The late antique spiritual anxieties and tensions, the art of the period and the politico-social evolution of the Dominate, for instance, are themes very well explored by him (in the context of the time the author wrote this book), but I think he also made a few oversweeping generalizations or conceptual mistakes in his interpretations. For instance, the rise of the Abbasid caliphate seems to me to be the a further reshaping of a new world made on the basis of the Roman and Persian empires rather than a final victory of Persia over Rome, even in a cultural sense, while the ideas over Roman identities at this time needed some improvements, namely for the Eastern provinces, but again that’s mostly a result of the age of this book.
Concluding, this is a historical masterpiece any one minimally interested in this period should read. It’s just a pity there’s no new edition. Perhaps Brown could write a kind of “sequel” called Revisiting the World of Late Antiquity or something like this?