The mistake I made was to read Massie's "Caesar" just after I read Colleen McCullough's book of the same title. The contrast is pretty big - Massie evidently enjoys confirming every rumour, and generally having as much sex and scandal in this book as possible. To be honest, Massie turns great historical figures into a joke. Decimus Brutus, the narrator of the story, has a love affair with Cleopatra, Clodia and Octavian (the young Augustus) There is nothing at all in any ancient sources to back this up. Massie's own opinion doesn't really come into anything - if there has been a scandal mentioned as a possibility somewhere in the sources, Massie confirms it and also exaggerates it wildly. On top of this, his detail is patchy and inaccurate. He puts Octavian forwards as Caesar's nephew, not great nephew, he does not mention politics or military force, and his characters are all developed through sexual relations with one another.
The book is OK, however, it is reasonably well written and worth reading for those who know the characters of ancient Rome. For those who don't, I'd reccomend just picking up a Jackie Collins - all the sex and no politics! That seems to be what Massie is aiming for in the first place.