I fully agree. The Confessions is an incredibly modern book, when I read it the first time I couldn't believe it was written at the time of the Roman Empire. Also, the text is full of wit, like when he describes time (“What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.”).
The latter half of the book is a bit trickier. Like the other commenter, his treatment of time was food for thought - not just for me but for philosophers and scientists for centuries to come. After finishing that chapter I got lost in Wikipedia learning more about it, eventually finishing with articles on general relativity (Augustine to Einstein... not what I expected from a 16 century old book).
Anyways, read Confessions. It's really worth it.