It's tough to say. I guess the general consensus from a mainstream perspective is if it's entertaining to you then it's a great story which I believe it isn't entirely true since what feels good might not be actually good.
For me a great story is about finding what the author is trying to say, understanding their intention, the purpose of the project first. It's more work than simply consuming whatever I'm consuming and move on to the next but when I understand those aspects, I can see/tell subjectively whether or not the author was effective and successful in their storytelling which in result, tells me, my own emotion aside if the story was good or not.
I feel like that's why a lot of new webtoons don't hook me anymore because they all feel the same at their core. I can feel that they had a story in mind but then they structured it in a way that fits the current webtoon model. It's fast pace, they try a hook at the end of every episode etc. It doesn't feel personal and intentional by the author, it's more like an automatism to fit in a mold and it can breaks whatever the author was trying to tell/build-up.