This is a remarkably detailed look at the 5th century which saw the dissolution of Imperial authority in Gaul, Spain, Africa, and eventually Italy herself. Bury rather powerfully refutes many of Gibbon's reason for the fall of the Empire in the west (a phrase he dislikes as imprecise), mostly by qualifying them and examining why the East did not suffer the same fate. For example, the Church is proposed by Gibbon as a destabilizing influence; Bury says that is indeed so in Egypt and Asia in the 7th century during the Muslim conquests (due to Monophysites), but in the 5th century the common religion (particularly in the West) tended to be a force for unification (though there were those pesky Arian barbarians...). In the main, he's quite convincing, and, while he is often as disapproving of Eastern and Church affairs as Gibbon was, he's generally more measured and often more interested.

And that's just the historical interpretation (a strong point of his work, as well as Gibbon's); the actual history is extremely detailed while remaining engaging. There aren't very good sources for the 5th century (the Empire falling will do that) but he does a remarkable job of reconstructing (and relaying the reconstructions of others) to provide a cogent picture of 5th century events.

Volume II isn't quite as good as the first - perhaps I just found Justinian and his endless wars less interesting. The criticism that Bury doesn't spend enough time on artistic and social history remains true. But it's still a very good book.