I first encountered the Confessions at University in the 1980s and have had the chance to finish re-reading it this year. It is a classic in every sense of the word where the ancient and modern worlds meet each other in total comfort.
While not an autobiography as such the Confessions (or at least its first 9 books) is a phenomenal piece of autobiographical writing, describing Augustine's journey from his childhood to his embracing of the Christian faith in the late 380s CE. There is an immediacy to Augustine's description of events and relationships in his life which make them feel that they could have happened yesterday and the psychological insight which the author brings to his narrative feels immensely modern.
Augustine had a profound impact on the shape of Christianity and western thought more widely. While, after reading the Confessions, you may not not still necessarily like Augustine or his beliefs but you can not fail to be moved by his description of life and his journey to a religious faith.
I rate R.S. Pine-Coffin's translation very highly. He is clearly faithful to the Latin original of the Church Father and does not insert unnecessary flourishes or employ an overwrought style. There is a new edition available, in the "Penguine Classics" series, from 2003.
Spiritual autobiography, conversion account, theological reflection, meditation, prayer, and biblical exegesis, "Confessiones" by the great Doctor of the Church, Saint Augustine, Bishop of Hippo, is one of the most profound, moving and beautiful works of Christian theology ever composed.
Third reading, and each time the depth of this work strikes me anew. Behind the autobiography, and in the midst of the praying, are amazing theological and philosophical ideas and questions. Everything is doxological.