The Bishop of Hippo was not, I think, a very likable fellow. He is certainly one of those whose stature in Western history is such that we are told we must read his various works, or at least one of them, most likely his City of God, in order to consider ourselves properly educated. His influence in Western Christianity is profound; he is, I suppose, its Plato, just as St. Thomas Aquinas may be considered its Aristotle. And Western Christianity has, for good or ill, profoundly influenced Western history, so I suppose he's entitled to his august status (tee-hee). But he has much to answer for as well.
He was evidently one of those loathsome men who, like Rousseau, reveled in what they thought to be their unworthiness, so much so that he felt compelled to relate it to us in detail. In his Confessions he flaunts his misdeeds, especially his sexual activities, which seem to have fascinated him after his conversion as much if not more than they did when he was a wretched pagan neo-platonist or Manichean. I don't think this can be said to be simply the style of the time, but in his defense it may be possible to claim that zealous converts and sinners who have lost their way and been, most ostentatiously, found, have always been inclined to air their sins in public with a kind of masochistic delight.
Of more significance than his flamboyance in this respect, however, is his relentless propagation of the view that humanity, and indeed this world in general, is wicked, contemptible, lost, consigned to the flames of hell but for God's saving grace, which the Divinity dispenses with a miserliness which is appalling but is thus especially gratifying to those chosen as recipients, and of course but for the salvation that was the consequence of Jesus' sacrifice (this grace and this apparently incomplete salvation exist somewhat uncomfortably side-by-side in Augustine's theology). Our evil and that of the world, and the glorification of the Civitas Dei as compared with the Civitas Terrena, are his primary "contributions" to our history and our culture in my not very humble opinion.
Just how miserable these contributions and their effect are and have been is, of course, the subject of some debate. It would seem to me unsurprising that such views may encourage the development of a priestly elite, a fixation on achieving a state of grace through various rituals, and the denigration of the world and all its pleasures to the point where providing for the worldly comforts of people is a secondary concern at best. All eyes must be on the heavenly prize which may await us, not on what is here. And that was the way of it for many centuries, and still is now in many cases.
It's a sad legacy for any man. It's possible Augustine didn't foresee that such thoughts would lead to the institutional Christianity which came to be. Like other Christian apologists, he would claim that Christian doctrine had nothing to do with the disintegration of the Western Roman Empire. He was busily writing away even as the Vandals were hammering at the walls of Hippo. They were good enough to leave Augustine's cathedral standing, though, and this no doubt was considered a sign of something good for Augustine and the Church.
We have in a sense been cursed with great men, or cursed by them. Too many of the great have been convinced that they know what is good and true, and have been inclined to seek the imposition of their beliefs on others. The great are absolutists, and see things as black and white, good and evil. They invariably believe themselves to be good, though, and those who oppose them to be evil. Thus Augustine waged his wars against the Donatists and the Pelagians. It's likely he more than Nero fiddled while Rome burned; what matter the Civitas Terrena?
But truly, Rome's demise in the West was well along by that time and probably could not have been prevented by even the most patriotic of pagans. Augustine's importance was not in the destruction of Rome, but in the creation of a new Rome, one whose ambitions were just as imperial but directed towards a universal dominion of another kind. That new Rome proved more lasting than the old, though there is no Civitas Dei.