As a teenager I read stories and novels by King (and Clive Barker). I really liked Pet Sematary, It and some of the stories, like Jerusalems Lot, and many of the film adaptations. After that I didn't read King for a long time, but when I did (e.g. some of his later novels at an age of around 33), I didn't like them anymore - it seemed to be a bit too much mannerist and the themes didn't interest me.
Because of the Elder Sign podcast I'm now rereading Night Shift. I liked the first story - Jerusalems Lot; it is much more Lovecraftian than Graveyard Shift. I like the letter novel-style and the gothic atmosphere. But it's still far behind Lovecraft's own stories for me. (I also read the postapocalyptic 'vignette' Night Surf, which I didn't like, but I'll keep on reading.)
After rereading Jerusalems Lot AND rereading the great story The Rats in the Walls, I honestly was disappointed in Graveyward Shift. It just doesn't work for me. Maybe it is also because I like rats and other rodents, so that is no horror to me (and a bat is totally different from a rodent being an insectivore with a totally different way of living, and many bat species DO live in cellars, but that doens't matter for the story of course). I liked the discovery of the trapdoor to the subcellar and the subcellar itself, the evoked image of a desecrated church and the '12 years darkness', but apart from evoke some atmosphere, King doesn't do anything with the cellar and it's old contents to give more depth to the tale, I think. Unless you are supposed to have read The Rats in the Walls and are supposed to infer a whole story there, maybe.
What I did like was the switch in sympathy, from Hall to Warwick.
After listening to the podcast discussion, I also think King made a parallel with the Lovecraft story in that the rats have the same sort of role: they lead the characters to the real horror. In Lovecraft the horror is the degradation of the protagonist into his cannabalist sectarian ancestry, in King it is the evil that rises in Hall. But, as you said, King isn't really clear about what corrupts Hall.
Lovecraft's tale is far deeper, complex and atmospheric than King's. But I think the short story collection Night Shift as a whole is interesting from a literary point of view, as you implied in the podcast episode, in that it shows how the young King is experimenting with styles and themes.