From grade school, we learned that books are categorized. Usually by a general theme and then by the author or editor. It makes life easy to be able to go anywhere, for print or even ebooks, and know that if you're in the mood for horror, look in the horror section. If you want a book on how to make balsamic chicken, go to the recipe section. And if you want a love story, go to the romance section.
As a serious reader for many years, especially of the latter genre mentioned, I do know there are a ton of sub-genres within the broad spectrum of romance - and even erotica. You have your suspense, your paranormal, your multiple partners, for example. This is still refreshing and even easy. Sometimes I bet you wish the rest of your life could be so easy to peg. I know I do.
What happens, however, when - as a serious reader - you want more than just a thriller to read? You want to explore a new author, but not just any new author. Let's say your life is dying for a little laughter. You want nothing more than to snuggle down with a glass of wine and a love story (or two) that will make you smile and even laugh out loud! Hey, guess what? It's hit-or-miss time. There is no definitive way to tell you if the ensuing story will make you laugh, cry, shiver or shock. Okay, maybe I'm going overboard. There are readers' reviews and maybe the blurb can give hints to the emotional content, but it's not always that precise.
There is nothing I can do about the bookstores out there, but that's okay. I have my own hovel of books, both print and e-pub, that I can swap around and order them in their own new category - Emotion.