The only thing every agent wants to find in her massive submission pile is a must read book. That one book she can’t put down.
We were recently discussing this during a BookEnds meeting. One of us (I won’t name names) found a submission that she was strongly debating. She absolutely loved the idea, but couldn’t get past execution problems. Ultimately, she wanted to keep reading because she desperately wanted to fall in love with the book, but in the end she could put it down.
Authors often complain that agents and editors don’t want to do the work. “If you loved the idea so much why wouldn’t you work with the author to make the book better?” The problem is that often you can’t.
If I have a must-read book with a slightly unlikable protagonist or some plot holes, I can fix those, because despite the problems, I still couldn’t put the book down. If I have a must read book with a slightly weak idea, I can tweak that because no matter what, I still couldn’t put the book down.
What I can’t do is make the book into something I can’t put down. Trust me. I’ve tried. There have been too many times over the years when I’ve desperately worked with an author because I loved her idea so much, but the problems allowed me to put it down. They got in the way of my enjoyment. I thought that if I could just fix those problems, I would make it unputdownable. Never happened.
In all likelihood an agent will always edit your book before going on submission. There’s always something that needs tweaking. But no matter what, before she got to that stage, she found your book so good she stopped all of her other work to get it read.