This is a carefully documented, but otherwise undistinguished history of Roman Empire from the accession of Diocletian (284 CE) to the death of Heraclius (641 CE). It is of course important to carefully document all the sources used in compiling a history, but it is equally important to develop an effective scheme to organize and analyze those sources based on some sort of unifying theory or theme. That is the difference between a compilation of events and a history.
The Roman Republic and then Empire, as with all nation states, under went a more or less continuous evolution from the foundation of Rome to the fall of Constantinople in 1453 (CE). During the calamitous Third Century this evolution was especially profound and rapid. When Diocletian assumed the imperial purple the empire was vastly different from the time of Caesar Augustus and even from the time Marcus Aurelius Commodus (180-192 CE). Diocletian was a reforming emperor who tried to stabilize the empire and the way it was governed. He realigned administrative boundaries often codifying changes that occurred during the breakdowns of the Third Century and tried to stabilize the economy by various methods including creating bans on changing jobs. In this history Mitchell alludes to this only vaguely and only in the middle of the book does he even mention that the Third Century was a time of evolution. In the same manner, one would never know from this history the later Roman Empire was considerably more than a continuation of the earlier Roman Empire.
Mitchell appears unable to identify linkages, note significant changes, or prioritize the information he presents. For example had he compared the Roman Army of Marcus Aurelius Antoinus (161-180 CE) with Notia Dignitatum which he mentions at least twice he would have discovered that the Roman Army had evolved into a very different entity than Gallo-Roman legionaries of the earlier empire. This is not a trivial quibble, but goes to the heart of Roman-Barbarian relations in the later Empire. Indeed the erosion of the capabilities of the Western Roman Army declined precipitously after inflicting a serous defeat on the Goths at the Frigidus River in 394 CE. This decline made the Western half of the Empire open to the out right take over of Roman territory by various barbarian groups. This inability to conceptualize patterns and trends prevails though out the book.