The Blue World is classic Jack Vance; a society descended from interplanetary castaways lead a relatively untroubled life on an inhospitable planet, but one of willing servitude to the Kragen, huge native sea monsters. See, the “blue world” is just that, a planet covered completely by water where the humans get by with only a few natural resources and the wisdom of their forefathers (which, in the great tradition of Vance's always wry sense of humor, they fail to fully comprehend).
Everything is fine until the mighty King Kragen, the largest of the sea monsters, begins to demand more and more from the colony in return for protection. When one man has had enough and defies the planet's semi-theocratic codes, everything falls apart. The population divides between the rebels and the complacent and major civil strife erupts–but if the rebels really are to destroy the beast, how can they do it with no source of metal for weapons, no knowledge of combat?
It's a fun, quick read full of Vance's signature speculative anthropology that fans will truly enjoy. The uninitiated could probably be swayed by this one (my friend Mike was), but maybe start with the jauntier Showboat World.