What defines great literature?

I’m looking primarily for an intellectual conversation about how we define and judge literature as a whole, especially within fantasy.

With the release of the latest installment of The Empyrean series by Rebecca Yarros, I have seen a lot of discussions amongst different Reddit threads calling these books bad writing and heavily criticizing the author, the readers who enjoy them, etc for liking them.

It stopped and made me wonder. From a very base level writing, especially fiction writing, is an art… art by nature is very subjective. There are artists I’ve seen who are known worldwide at a glance that I could tell you I barely even register enjoyment for. But, it’s still art and is still valuable.

Do we have an art of rules that makes a book a good book? Do we have a certain style or cadence of writing that is the only acceptable way? What makes a reader wrong for enjoying something? Isn’t the point or the thing we should celebrate in this day and age is that we live in a world where we can pick up a book and live out dragon riding dreams?

There’s so much criticism for these authors who have built huge worlds and concepts together. Granted, you get repeat themes, but you could say the same for music.

Just looking for a general discussion of why we take this viewpoint. Have a fantastic day!