To answer that question, a number of literary agents have contributed their ideas to a tumbler wish list of books they would like to see. Most of their ideas are for novels, though some agents mention memoir and non-fiction. If you have a book, one you are working on, or a book you are about to embark on, the list will interest you. There are some generic wishes, but many are specific. Some maybe even surprising. Here are some examples:
I like YA contemporary with a lot of pathos. I want MCs with big adult-sized problems that they’ve got to figure out on their own.
Also, I’d love a mystery/thriller/horror with a strong anti-hero. Think Dexter or Lost
A touching, heartwarming mother/daughter story with a fresh hook. And a side of tissues.
YA contemp. w/ unique hook (less “coming of age because of life” & more “no choice but to come of age because THIS HAPPENS”).
In their wish list, some agents mention stories they don’t want–because they probably get them all the time. Follow the link, and at the bottom, click the next arrow. There’s quite a few posts.