Arrian was a Greek historian of the Roman Empire writing 400 years after Arrian lived. His work concerns only the reign of Alexander and is primarily a military history. Arrian was writing long after the events, but he appears to have done his research and to be good at distinguishing between reliable and unreliable versions of events. The book, however, does not really have a great deal of literary merit, although it does paint a clear and one feels relatively accurate portrayal of its subject. Arrian admires Alexander, but is not afraid to criticize him, but he is clearly not in the top tier of ancient historians and I would put him behind such people as Livy and Polybius, let alone Thucydides and Tacitus.
The book's subject is more interesting than I anticipated and I did not expect to find it dull. Alexander's military prowess is every bit and more what you would expect, even given probable exaggeration. He is brave to the point of insanity at times, and good at founding cities, but he appeared to have almost no interest in either administration or enjoying the fruits of his conquest. Instead, his campaign went on into India, as everyone knows, but how insane that was emerges from reading a book like this. You realize as he conquers people after people along the way that going to India, would be like trying to conquer the moon today if it were filled with moon-men. Conquest became conquest for conquests sake and Alexander was like a person possessed. Its a fascinating story of a man who changed history and whose life was short and brilliant and obsessive.
A good read. But you do not need to read about Alexander through Arrian. He is a good choice, if like me, you enjoy reading ancient historians.