This isn't Gilligan's Island. It's not even Lost. Jack's wildly superstitious and violent group of boys, who are willing to kill one of their own with their hands and teeth, is as far from ideal, or utopian, as you can get. In our book, that makes this dystopian literature. (Can't get enough dystopia? Check out George Orwell's 1984 and Aldous Huxley's Brave New World.)
This also isn't Treasure Island. Sure, Lord of the Flies is an adventure, as we see how well (or how poorly) the kids survive on their own. But despite its focus on suspense and physical danger, Lord of the Flies is not the rollicking kind of adventure narrative that you get in, say, Treasure Island. Nope, Lord of the Flies is much more interested in subtle commentary on warfare and human nature than on the kids' day-to-day efforts to survive on an isolated island.
This also isn't Survivor: Lord of the Flies. Jeff Probst isn't around to explain to us what challenges face Ralph, Piggy, or Simon, and people tend to get viciously murdered rather than voted off the island (even though Ralph does try to make it democratic). As such, it's an excellent example of literary fiction, a genre preoccupied more with characterization and symbolism than with plot or straight-out explanation.
And the focus on character development brings us at last to coming-of-age. As the boys around him freak out, we see Ralph develop from a smart, brave, fun-loving kid into a hunted man who preserves his moral perspective even as the island falls into chaos. He manages to survive long enough to be rescued without (totally) giving in to their hysteria, something we're pretty sure we couldn't manage. We're not totally certain that Ralph has gone from childhood to adulthood—we're not even really convinced that William Golding thinks that children and adults are so different—but he's definitely learned some hard lessons about human nature.