I have seen Shadowlands and liked it, although not since reading his writings about that time of his life, so I don't know how I'd like it now. I should rewatch that.

The chronology of how he wrote his fiction basically goes Narnia, Space Trilogy, Till We Have Faces, and while I do think Perelandra is worth a retry just because the setting is gorgeous, I highly recommend Till We Have Faces because it is the book where Joy came through and told him to fix all the women. It's not perfect but he grew in interesting directions. It's also just a really good book, it's a retelling of Cupid and Psyche which is not from the usual viewpoint and does not go the usual directions and is not, to my memory, in any way overtly Christian.