I find a book handsome not because it necessarily differs from the standard template. You don’t want a book design that says, “Look at me! I’m designed!” You want a book design that says, “Dive into this text.” So it has to be inviting, but also capable of becoming transparent once you’re in it. Like a cool pool on a hot day. You splash in, you scream delightedly, and after a few seconds it feels normal and you can focus on hitting your friends with foam toys or whatever. I like a design to complement and enhance but not upstage or distract from the text.