I'll not play coy and pretend spoiling 'Salem's Lot is even possible at this point; if you care to read it, you already have.
Perhaps the thing that most stands out for me in the "not remembered" category is the sheer richness of the prose. Stephen King, at this point - and I'm not saying that he isn't now - was a careful craftsman and artist with words. Long and not-at-all-boring passages are spend on psychological and sociological analysis, sheer description, and such. And the book isn't padded at all, the way that some claim King's books to be; everything - and I mean everything - in it is necessary and contributive to the whole effect.
King introduces characters slowly, bringing in some fairly major characters fairly late in the narrative - and yet, somehow, this works. The pivotal character of Father Callahan doesn't really enter the plot till well over half the book is past, and yet he is perhaps the best developed character, with the most interesting and meaningful story arc.
For those who need reminding: he is a middle-aged Catholic priest, slumping into alcoholism, largely due to the banality of his life. He entered the priesthood wanting to fight Evil, and finds himself dealing instead with the dull and repetitive evils that make up so much of human life.
When the Fearless Vampire Hunters come to him, he is more than prepared to believe: he has seen the strange things happening, and he wants to finally fight Evil. And, armed with holy things, he works a minor miracle or two in the fight ... and then gets his comeuppance in a standoff with the head vampire, Barlow. Barlow holds the boy Mark Petrie; Callahan holds up his cross, and it glows brightly and forces Barlow to move back; but he still holds Mark. He offers Callahan a deal: if the vampire releases Mark, will the priest throw aside his cross? To prove his good faith, as it were, he releases Mark.
And Callahan's faith fails him. He does not put down the cross ... and its bright light fades, and Barlow, rather than drinking the Father's blood, forces the Father to drink his.
Returning to his church, he cannot enter. The doors fend him off with blue fire. He leaves the town on a midnight bus, obsessed with his uncleanness...
But hidden in there is Barlow's mocking comment: "If you had cast the cross away, you should have beaten me another night. In a way, I hoped it might be so. It has been long since I have met an opponent of any real worth."
There is a deep morality here that I find very satisfying. Yet so much of the book is about the power of evil, in both its capital-E vampiric form and its small-e banal, human form. There are plot elements which might be described unkindly as soap-operatic, or more honestly as slices of village life. And the main character of the book emerges not as the vampire, nor the Fearless Vampire Hunters, but the village itself, the Lot, which we see in a series of panoramic and close-up images of itself and its people, and if the Lot dies at the end, well, so do all good things in this world. Some see in 'Salem's Lot a condemnation of the people of a small New England town; it seems to me rather a love letter to those people and their towns. While they are flawed and often petty, there is not a real villain among them.