I've read this book multiple times and its mythic images have deeply impressed me. The image of Orual reading her “great work” at the end and seeing what she is really saying is powerful and rings true with much that I have myself experienced in life. Our true motives are so often hidden from us, and coming face to face with them can be a shattering experience. The message of hope and reconciliation at the end is reassuring and I believe also true to the way things are in the deeper reality. The divine world wants us to become worthy of standing in its presence, but we have to do some hard work to get there.
I think it's better not to see the novel as an allegory but as an imagination which embodies truths about the human soul and spirit. In that regard I think it's Lewis's finest work.