The Confessions is routinely called the first autobiography in the Western tradition. That description is not wrong, but it sets you up to read the book badly, because it suggests Augustine is addressing you. He is not. He is addressing God throughout, in the second person, and you are overhearing it. Once you notice this the book changes shape entirely.
The structure nobody warns you about
There are thirteen books. Nine of them are narrative — childhood, the pear theft, Carthage, Manichaeism, Milan, Monica, the garden, the conversion, her death. Then the narrative simply stops, and Book X turns to memory, and Books XI to XIII to time, creation, and an extended reading of Genesis.
Most readers are ambushed by this. Some conclude the last four books are an appendix bolted on by an author who lost his nerve about writing a life. I think that reading is a mistake, but I understand it, and if you come to the book expecting a memoir you will feel the floor give way around page two hundred.
The turn makes sense if the book is a prayer rather than a life. Having confessed what he was, Augustine confesses what God is — and the question of time in Book XI is not a digression from his conversion but the same question at a different scale. What is it to be a creature who exists in succession, addressing one who does not? He has been asking that the whole time.
What holds up
The psychology. Sixteen centuries have not dated the account of divided will in Book VIII — the experience of wanting a thing and wanting not to want it, of commanding your own will and finding it does not obey. Augustine's analysis of why the mind can command the body and be disobeyed by itself is still, as far as I can tell, unimprovable.
The pear theft in Book II is the passage people find excessive: a great deal of anguish over some stolen fruit. But he is precise about why it disturbs him. He did not want the pears; he threw them to pigs. He wanted the transgression itself. That is a much stranger thing to have discovered about oneself, and he is right to sit with it as long as he does.
And the famous line at the very opening — that our heart is restless until it rests in God — is not a decoration. It is the thesis, stated on page one, and everything after it is argument.
What is hard
He is a rhetorician by training and it shows. The prose apostrophises, piles clause on clause, and asks questions in bursts of five. Chadwick's translation is the one I would recommend for a first reading precisely because it resists the temptation to smooth this out; you get the insistence rather than a tidied paraphrase.
The treatment of Monica will trouble modern readers, and the treatment of the unnamed woman he lived with for over a decade — the mother of his son, dismissed in a sentence — should trouble everyone. Augustine does not see her. It is the most serious blind spot in the book and it is worth naming rather than passing over, since the book's whole method is the examination of self-deception.
Whether to read it
Yes, and not as history. Read it as the account of someone discovering that he is not transparent to himself and that God is not therefore inaccessible.
If you bounce off Book I, start at Book VIII and read the conversion in the garden, then go back. The opening books reward you far more once you know where the man ends up. And be ready to stop at Book IX and return later for the rest; there is no shame in reading it in two goes, and rather less in that than in pretending you found Book XII straightforward.