I think that's artistic license somewhat. He obviously wasn't averse to violence to achieve his goals (but you could say that Caesar's assassins demonstrated what happens when you forgive and spare your enemies) but he's positively cuddly when you put him beside other figures like Sulla.

Suetonius says he was "well favoured and charming" throughout his life but a bit of a slob. He was "moderate in his habits, and without suspicion of any kind of vice" aside from his habit of gambling and predilection adultery and young virgins (but I mean who isn't into sleeping with other men's wives and deflowering young women, c'mon).

The impression I get is of an incredibly disciplined, smart, ambitious, and coldly calculating man who wanted what he thought was his by (adopted) birthright and that he was a better man than any of his senatorial peers (and demonstrated it quite well). His participation in the proscriptions show that he wasn't averse to killing for his goals yet he also didn't kill for no reason - he purposely spared Lepidus despite an attempted coup. Lepidus held the office of Pontifex Maximus which Augustus certainly wanted to give him greater legitimacy as he remade Rome, instead he waited until Lepidus died peacefully in exile.

He was a traditionalist, a hypocrite at times, but someone who saw that the Republic was clearly broken and that he offered a chance to stabilize the state. He was smart enough to recognize how to do so without antagonizing the senate and manipulating everyone so that ultimate power was handed to him in Republican trappings. His self-control is amazing, he was named heir to Caesar's will and had a claim on his faction (currently lead by Marcus Antonius). But recognized the long odds of a direct challenge and instead sided with the senate against Antonius. Then when he recognized he couldn't defeat the combined forces of Antonius and Lepidus he made common cause with them against the assassins.

Cassius Dio's records an incident where the emperor was dining with Vedius Pollio who had a reputation for cruelly punishing his slaves (feeding them to eels). When a slave broke a crystal cup during a dinner and pleaded for his life, the emperor made a point of ordering all Pollio's cups to be broken - setting a precedent so the host could hardly kill a slave for the same thing the emperor did. Pollio clearly was in his right to throw his slave (his property) to the eels (or lampreys) yet the traditionalist Augustus felt this was certainly inappropriate and excessive. That doesn't sound to me like a sado-masochist psychopath.