Make no mistake: Confessions is not a novel. Though this tome at least has a plot, which is more than we can say for a lot of books, it is also a piece of philosophy. So it's not exactly a page-turner unless you are really compelled to find out the fate of Augustine's soul.
The fact that Confessions is translated from Latin can make the language sound kind of clunky and basic sometimes, but don't let that deceive you into thinking that Augustine is just stating the obvious. Remember, Augustine makes the same mistake with the language of the Scriptures. Sometimes it takes a few paragraphs, or a step away from the text, to really see where Augustine is going with what he's saying. And some knowledge of the historical and philosophical contexts certainly helps us better understand why Augustine finds these issues of God, sin, good, and evil to be so important.
This book also gets a high rating because there are a lot of Biblical and philosophical allusions in the text. You definitely don't need to understand them all, but again, it really helps if you know a bit about what he's referencing. If you have an edition of the book that footnotes the passages quoted from the Bible, your life will be way easier… even if you just use these footnotes as a heads-up that he's citing something at all. You might also want to keep that ol' internet handy so that you can quickly look things up if necessary.