I was never into "reading" mainstream horror but during times when I did a lot of driving, I did listen to a huge amount of audiobooks. Mainstream horror was far more available from the library than any literary horror would ever be. So I will start with Stephen King, I have probably listened to almost everything he has ever written, except the Dark Tower books. I started a few on audiobooks and could not stand them, it may have been the narrator.
Most of his output is very "workmanlike". Gets the job done but without any artistry, or even soul. Most of the sentiments seem false or forced. There is a good sense of regionalism, and in fact, this may be what he should have focused on as I perceive it as the most artistic quality in his works. While his characterization seems impressive at the beginning, eventually you realize that it is all the same, with a couple of notable exceptions like The Running Man, the Long Mile, and a few others; often in the Bachman books.
King's novels that I did really enjoy, still not literature, are the following: 'Salems Lot (my favorite, although this may have some germination from watching the TV movie at 13 and being floored by it), Pet Sematary (with its logical faults), The Shining (with its rather stupid topiary garden section), The Body (probably this and 'Salems Lot are the best things he ever wrote), I liked Insomnia and Revival (the last probably because he at least tried to do a cosmic horror story). Misery, Dolores Claiborne, and Gerald's Game are all good (except the goofy thought transference thing in the last 2 of them) but these books are not really typical of him. I have enjoyed portions of many of his books but there is almost always a point where it becomes deus ex machina or even simply childishly moralistic or cheesy. I also find his his early short fiction rather laughable and wonder how he parlayed a literary contract based on that pablum.
I hated The Stand, Cujo, Firestarter was dumb, at least half of IT sucked (for god's sake the horrible bathetic "fat kid into a buff archetect, et al" is enough to make one vomit in one's own mouth), and many others, although, as stated above, portions of most of them were certainly enjoyable in isolation. Often the proble with his works start when the supoernatural comes to the fore, The Outsider was exilerating until the supernatural "explanation" became the focus. The novel totally becomes goofy at that point. The Mr. Mercedes novels are realativel enjoyable on a banal level right up to the introduction of the supernatural. It is amazing that the "King" of supernatural fiction is actually terrible at writing about the supernatural. He is really just a typically optomistic humanist, like Speilberg, but has an affection for horror and SOMEHOW became the most sucessful novelist of all time. There are dozens of books that I did listen to and probably could comment on but can see no reason to do so.
The problem for us discerning readers is that King, with all of his negatives, is really far better than much of, but in no way all, mainstream horror. I still listen to novel after novel only to stop most of them an hour or two in because of the sheer banality of the writing/concepts/characterization. If I have to hear about any more sublimated alegories of middle class stresses translated into "supernatural horror" I will have to have a true scream.