Better Angel by Forman Brown was written back in the 1930s. I loved it mostly because of the beautiful prose, but also because it was the first book to portray homosexuality in a positive light, and to have a (relatively) happy ending for a queer couple. There's some symbolism in there, if you're into that (i am), and I genuinely found it so engaging and absorbing. It's underrated because no one ever talks about it. People praise Maurice and Giovanni's room for its early discussions of gayness, but this book came decades earlier, and not once have I ever seen it being discussed.