Antony and Cleopatra by Colleen McCullough
I started reading this series my freshmen year of high school. This should be the last one - especially since I originally thought the one before this, where Caesar dies, was the last one. While Caesar's death definitely was the end of a certain era in Roman history, I think it probably was good to include this part of history in the series as well since it isn't until Marcus Antonius is dead that Octavian really is the undisputed ruler of Rome, and becomes Augustus and the first Roman emperor.
The novels is in this series tend to be long - I remember the first one I read, I enjoyed immensely, but I also skimmed through all the letters because those got kind of dull and long. Fortunately there aren't too many letters in this one. Of course everyone knows the basic jist of the story, but McCullough does a good job of adding in the details, exploring how the propaganda may have worked and mentioning all the minor characters. Seriously, when reading these, it sometimes seems like everybody in Rome has the same name almost or they all have the same three names in different orders. It could easily get confusing in other hands.
So basically, McCullough definitely has the history part down. Therefore, how much someone enjoys the story basically has a lot to do with her portrayal of her characters - if you are sympathetic say to Cleopatra and Anthony (and who wouldn't be - epic love story), then you might not be too happy with the way things go. Especially Cleopatra. McCullough definitely has her moments where she treats all her characters with sympathy and is understanding of their weaknesses, but Cleopatra is probably portrayed in the least favorable light. Octavian, on the other hand, she is obviously very fond of - I guess I can see why, he brought reform and peace to Rome after decades of war, both civil and expansionist. It was actually kind of nice to see things from his perspective for once (one of the other novels I read on this subject was The Memoirs of Cleopatra - guess who is kind of an evil monster) but I still wish Cleopatra hadn't come off as quite such a villain.
Maybe it's just me, but while of course I know of Augustus as a historical figure, he usually seems so much less interesting than Caesar or Anthony or Cleopatra. I think it's just between Caesar's dramatic murder and then the whole Anthony and Cleopatra story (as well as the suicide by snake), it's hard to compete when it comes to taking over the popular imagination. Peaceful reigns aren't exciting to portray in movies although they are good for the people experiencing them.