People's reactions may be "I like the final covers better". I get that, I think I do too. But I suspect that's because they're more like what we expect from book covers. They're safer and less experimental. A lot of times our aesthetic evaluations are just based on what seems more familiar—that 'mere exposure' effect—and we find post hoc reasons to justify a gut reaction. I'm not even sure that's a bad thing, from the publisher or the author's perspective: they just want a quick visual shorthand to tell people that a book might be for people like them. They're not trying for much more than that. But I want these designers to not be that cynical, and keep trying new things even if they just run up against brick walls, because that's the mechanism that slowly evolves visual design.