What the writer will hear from one of the persons at the other end of the process: "The biggest problem with this book was....and then there's....and also....but the rest is pretty much OK, I guess."
With experience, you realize that this is going to happen, and brace yourself, but it's never as pleasant as the fantasy of being told the book is great, it just needs some milk wiped off its upper lip and its collar straightened.
For that, you have to depend on the alpha readers and later readers.