Stephen King is a much better short story writer than novelist. In On Writing, he explained that he opposes what he calls "plotting," by which he basically means figuring out ahead of time where the story is going---which explains why the longer the work of his, the weaker (if not outright awful) the ending tends to be.
His short stories tend not to suffer from this problem, both because plot is not as crucial to a good short story as it usually is to longer literary forms; and because, where it is important, structuring a shorter piece does not seem to overtax his ability like a novel does.
There is a more serious dimension to many of King's stories than one might expect, and I like that about them. For one thing, there is a strong moral sensibility to his writing, and while I disagree with this moral sensibility (it being strongly informed by his Methodist upbringing), I like the fact that it's there at all. Too many writers these days are amoralists, whether explicitly or by omission, so it's somewhat refreshing to read a collection of stories that contains a little moralizing (though it's usually pretty subtle, almost more a mood pervading the piece than an obvious point to the story).
Another thing I like very much about King's writing is the sort of self-reflective nature of it, the examination of what it is that a writer is doing as an artist---namely, recreating the universe in his own image. This comes across most strongly here in the story "Umney's Last Case" (though King has dealt with it explicitly elsewhere as well, notably in The Dark Tower series). But the implication is present in the rest of the collection, growing out of the interconnectedness of detail and the integrity of style, which communicate the feeling that all of the characters in all of these stories inhabit the same world, and that it's Stephen King's world, a fact of which he is well aware and wants his readers to be aware, as well.
Several of the stories here are attempts to utilize the style of other writers, such as H. P. Lovecraft in "Crouch End" and Arthur Conan Doyle in "The Doctor's Case". These attempts are surprisingly successful. "The Doctor's Case", for instance, is a Sherlock Holmes story in which Watson solves the case---a twist that Conan Doyle himself may never have employed, but which King manages to pull off very much in the spirit of the original Holmes stories. At the same time, King makes these stories his own, bringing them into his own artistic vision.
There are several stories here that are basically adult versions of Scary Stories to Tell in the Dark---stories about downpours of carnivorous toads, incredibly long fingers poking out of bathroom sink drains, and chattery teeth with a will of their own---but even these are pretty fun because King does not take them too seriously, but is perfectly aware of their absurdity and tells them with tongue slightly in cheek. If he tried playing them completely straight, the readers' ability to suspend their disbelief would become a real problem. Thankfully, he does not.
Finally, there is a non-fiction piece about little league baseball, to which King brings his fiction writer's sensibility and makes it surprisingly suspenseful, and meaningful.
All in all, a solid collection of work, and probably one of King's best books.