While the Dark Tower is an epic in the grand tradition, I think that King will in later years be recognized, as it slowly dawns on people, not for the Dark Tower (which will have readers until forever comes and goes) but instead for doing something that in literature had not previously been done EFFECTIVELY...
Desperation and Bag of Bones.
In one he reverently and realistically bridges the gap between man and God even so far as to make God the unseen protagonist ("What do you think will happen if it is not stopped?"
-David's mouth opened wide. "It will spread," he whispered.
"No," said the man in the sunglasses. "It will overextend itself and die. That is what evil does."
-"Then why can't we just leave?" David asked, "Why do we have to fight it?"
--The sunglasses turned on him. "Because it is an abomination, and your God commands it."), and in the other he recreates the best of what Mary Shelly and Bram Stoker and all of the Victorians were trying to accomplish: He wrote a totally immersive ghost story that was, according to EVERYBODY'S CRITERIA AND BENCHMARK, Literature!!!
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Do I love the Dark Tower? Hell yes!
Do I love the Stand? You betcha!
(Oh, and Blofeld--The TCMan's actions at the end of the stand were to reiterate something about the nature of evil, whether it be Tak or Flagg or the King or George Stark, and that is that evil will always have BLIND SPOTS, spots where its arrogance or its power cannot see that the seeds of its destruction are sown...and the TCMan was the bringer of that which is another theme in King's works, which is the idiot savant having a touch of the divine in them, or at least a part where the divine can pull and prod.)
Of the old books, Salem's Lot is my favorite.