For one it eschews the "great man (or woman)" sort of history and focuses instead on culture. In the 1990s history had turned away from "great person" biographies and the focus on war and grand events. It was about the people and culture. This was, of course, an important correction. In some cases it maybe goes too far in this direction of ignoring the kings and queens and such altogether. Some may have that impression about Hourani's book but I do not think that would be accurate. So often Westerner's read about Arabs ONLY in the context of rulers and also as bit players in some Western story. This book will have none of that and it is incredibly detailed and focused.
Within the cultural focus mentioned there is a hyper-focus on the role of Islam. Indeed the book basically starts with the origins of Islam. History before Islam is treated as prologue and an extremely brief prologue. The one great man there is detail on is the Prophet Mohammad (and if you are going to pick a single towering figure you cannot find one larger). Yet even the great Prophet isn''t really the focus; the beliefs he espoused.
The history of Islam is an enormous part of the history of the Arab people. Especially in the early third of this book the religion is the backbone of what is laid out for the reader. If you come to this book looking for detailed discussions of Arab expansion East or West or the battles fought and the men who led? You are going to be disappointed. In part this may be because Hourani knew that if you start down that road you, out of necessity, start talking about Byzantium, the Sasanians and others. This is a book about the Arab peoples and he shows great discipline in keeping it just that.
He does a great job putting you into the ancient world at various points in time and locations. When the book arrives in modern times it outlines policies again, not getting tied up in personalities. If you start discussing independence and the receding power of Britain and France in too much detail the focus might be lost. It doesn't happen. The book never bogs down in personalities.
This isn't to say that there is anything wrong with biography or history books about wars and significant political events. This just ISN'T any of those and it is valuable because of that. This is also not a "popular" history even though I believe this book was a best seller. This is history history so be prepared to wade through detail and repetition. It is meticulously sourced and indexed. If you cannot bring yourself to read it in one fell swoop it is definitely something you can return to.
Doubtless, in the over 30 years since this book was published there have been changes, revisions, in the history. I don't know enough to tell you what these are but it is true of most books of history. Nonetheless, this is a fantastic place to start in learning about the Arab Peoples.