Thematically modest but logistically ambitious, this seagoing science-fiction adventure was originally envisioned as a Roger Corman-produced quickie. The thrifty mogul demurred, concerned about the budget; the film eventually cost $175 million. Is the money on the screen? Sort of: WATERWORLD is simultaneously overproduced and insufficiently imagined. In the future, the polar ice caps have melted and flooded the Earth. The Mariner (Kevin Costner) has adapted well to this watery new world, sailing in a specially designed trimaran and salvaging treasures from the sea. At the Atoll, a floating armored settlement, he trades soil for a plant and some water but runs afoul o...