Levine says he thought shooter games needed a similar kick. The genre had progressed surely but slowly, and he wanted "BioShock" to lurch things forward. Conventional shorts had linear layouts. A player could map them, he said, by "unrolling a ball of string." He wanted to build Rapture as a city to explore in any direction, to wander in and crisscross. Typical shooters locked players in a room for shootouts with level-ending boss characters. The "BioShock" Big Daddies will roam, and the player hunts the bosses and picks the fight. "You decide where [the fight] happens," he said. "You set up the ambush. It's a tough fight. … These are bosses that just live in the world. You determine the rules of engagement." He says there's more.