It tells the story of a transformative year in the life of Devin Jones, a young man of college age who takes a summer job working at the North Carolina seaside amusement park Joyland, in the early 1970s. As the sweet, nostalgic story is gradually populated with a cast of interesting characters, King's trademark foreshadowing reminded me against my will that, of course, innocence cannot endure forever, and with growth comes loss. Devin works at finding his niche, and comes to enjoy and even excel at the arduous task of "wearing the fur" of Howie the Hound, the park's mascot. The pleasure he sees on little children's faces makes the burden of the hot, sweaty costume worthwhile to him.
But the park (and appropriately, its Horror House ride) is haunted by the unsolved murder of a young woman a few years before. The crime, by this point, has come to be neglected for lack of leads, until Devin's curiosity is aroused. Well, no good can come of that! I found myself almost wishing that he would let it drop, and the razzle-dazzle illusion of Joyland could persist, but that isn't how the story, or I suppose life, goes. It really didn't spoil the mystery for me when I got a frisson of suspicion on first meeting the person later revealed to be the killer. It's just that good a story in so many other ways.
I'd say that this would be a great Stephen King book for people who think they don't like Stephen King books, but want to try one. The minimal supernatural content is actually benign, and the story, as told by the Devin of 40 years later, is heartbreakingly universal.