Not a King fan, but here is what does appeal to me about him ...
First, Stephen King is an amazing writer. His prose and style of writing is immersive. Whatever he writes about is believable.
Second, Stephen King creates a world that has its own logic and that you enjoy visiting and inhabiting even if you don't really like the book or plots that are going on.
Third, the characters Stephen King populates his world with and his writing about them and dialog makes you care about these people and want to know what happens to them and that they get protected and rewarded if they are good or punished or destroyed if they are evil.
Then, a trick Stephen King seems to me to employ, that causes me to be interested in his stories are that he creates the world as normal for maybe 20% of the story before he springs any supernatural stuff on you. That really bugs me. I start to like the story, and then things just get weirder and more often than not I drop the book or stop the movie/series because I cannot stand the nonsense or suspend my disbelief.
Though I am not a big Stephen King fan, I respect his skill in storytelling and characterization, and I also like his politics and disdain of Donald Trump. That is probably more than anything what got me to start watching "The Outsider" on Amazon, which is not really that great, but it is compelling and suspenseful.
I'd love to read King if he wrote a real novel without superstitious and paranormal stuff ... in general that is just not something I care for, but I have to respect a master than appeals to so many others.