I appreciate people who are civil, whether they mean it or not. I think: Be civil. Do not cherish your opinion over my feelings. There's a vanity to candor that isn't really worth it. Be kind.
My friends and family have been so well trained that they know I really mean it when I say that I don't care if the review is good, because that can be as dangerous as when it's bad. It's less demoralizing, but it can be just as confusing.