Cassius Dio or Dio Cassius is with Tacitus and Suetonius the nearest, just about we have to contempory sources for the early empire and, in particular for the age of Augustus since I was researching for my book on King Herod who was as friend of Augustus and of Marcus Agrippa the Emperors chief supporter and also a friend of Herod. As Roman writers though sometime after the events they give us the thoughts and observations of people at the time. Such sources are, therefor very valuable to the historian. Cassius, of course is much more detailed and wrote voluminously. The section on Augustus gives us a rare insight into the character of the First Emperor.