I have just finished Till We Have Faces, and now begin to get why people consider it not only Lewis's masterwork, but even the greatest novel of the 20th C. Yet it is so easy, in complete contradiction to Lewis's intent, to think repeatedly of other people who really, really need to read this book.
There is a dream/vision in the second part - very medieval, as in "Piers Plowman," "The Dream of the Rood," or Dante's Divine Comedy - in which Orual has many of her personal explanations of the relationships and motivations of her life from earliest ages turned on their heads. It is so easy to resort to those explanations of what relatives, early friends, bosses, and mentors did that we have cherished these many years. For adult relationships I have already recognised how mixed the blame might be.
But I flipped the narratives for stepfather, brother, and to a lesser extent a few others. I still cling to that 90%...60%...20% they did wrong, but am at least having a go at it. You should encounter the book in your own way and I will say little more. But should you attempt it, reading the myth of Cupid and Psyche sometime before the last section of the book, or reading The Four Loves in advance or in parallel, or reading Aristotle and some Plato would be helpful.