Okay, some of my friends who read it told me they liked it, and even what they liked. (Several thumbs up so far for the scene in the shell hole.) I got an email from a stranger, a bookseller, telling me she'd liked it, which for me was something new and wonderful. I should be content with this.
Apparently, it's not enough. And I think I know why. It's because I want validation. Being paid for a book and having it published isn't the same sort of satisfaction as knowing the book was entertaining and that you made people happy. Also, that need for validation? Is much, much stronger when I'm in an uncertain place, for instance when I'm finishing a big project, like I am right now.
I think the need has a different angle as well. I can't control the overall sales of the book, but getting feedback reminds me I do have control of one thing - the story. I made the story. So it's important to know if the story achieved its purposes or not. That, too, reflects on the current project.