Possibly I had avoided it because St. Augustine has an unfortunate reputation in the modern Western church and culture for being entirely too strict, and particularly for being anti-sex (even within the context of marriage).
I found something more subtle and intriguing than I had expected.
The first surprise should not have been surprising, but... I don't expect a book written by a Christian that far back to be what we would now call "confessional literature." It's not a list of sins and forgiveness; it's the story of a life spent searching for truth, through pleasure, through ambition, through excellence, through science and philosophy, and finally finding its home in Christ.
"God, you have made us for yourself, and our hearts are restless till they find their rest in you."
It's the modern sensibility that startled me. Augustine writes very little that could not have been written by someone just before the advent of post-modernism or the rise of modern psychology. It actually reminded me strongly of reading Joseph Campbell: a very bright man working from what he has--which is less than what we have now--towards the same goals as ourselves: self-knowledge, knowledge of the world and how to live in it, knowledge of truth.
I'll give an example. Near the end, Augustine spends pages dissecting memory. What it is, what it is not, how it may function. I read this with a shock of recognition. He sounds (minus the translator's unnecessarily archaic language) much like a researcher writing an article on cognition or consciousness. It's clear that he would not find their ideas strange; even the discussion about how much of our emotions, memory or reasoning power is biological might not throw him.
I found his description of his journey to faith both funny and moving. He does not leave out much, either bad or good, and it is beautiful to read about such a faith journey, of someone whose greatest gifts were also his greatest stumbling block, of an intellectual who arrived at the truth slowly rather than through some flash of revelation, of a scholar whose need for recognition blinded him to the wrongdoing he himself was committing against others.
I quite enjoyed the entire book... until the last ten pages or so. I suppose it is reasonable enough that a man who had live Augustine's life might find himself needing to be severe in his limitations on wine, food, curiosity and sexual behavior/thoughts, but it was all far too much like Christians I have known who measure their godliness by how much they can do without. Ugh. And after spending most of the book talking about how God is more than the things in the creation that we love, and yet all of creation displays him! It felt harsh, and very nearly hypocritical.
Well worth the time of any interested reader, though, certainly, and I am very glad I read it.