Soon after, you come across a syringe which, after an oddly willing injection, grants you Electrobolt, the ability to fire Palpatine-like arcs of lightning from your hands. Abilities such as these are involved with both combat and puzzle-solving in BioShock. Electrobolt stuns enemies momentarily, priming them for a killing blow, but can also be used to spark life into reticent machinery. A fire-casting ability can be used to, well, light guys on fire, but also to melt ice that is blocking your path. After seeing himself perform this superhuman feat, your character becomes slightly freaked out and faints. From the floor, during a return to consciousness, you glimpse a Big Daddy and a Little Sister.

The bizarre pairs of Big Daddies and Little Sisters are a crucial part of BioShock. Little Sisters--ostensibly young, vacant-eyed girls--are the only individuals capable of obtaining Adam, essentially the currency of Rapture used to purchase the upgrades that become instrumental to gameplay. Big Daddies--massive, iron-clad, drill-armed hulks--are the Little Sisters' protectors, and will go to any lengths to ensure no harm comes to their petite charges. Trailers and promotional materials for the games have painted, as the characters' names suggest, a bizarre form of a father-daughter relationship in the pairings.

The story behind the Little Sisters is sure to be a major plot point in BioShock, and the player's choices surrounding them will have direct gameplay implications. At numerous points throughout the game, you find yourself in a position to either let a Little Sister go free or to harvest and acquire her Adam--which you must kill her to do. During the first instance of this frustrating moral choice, you are being pelted with arguments from two opposing sides about the nature of the Little Sisters and the importance of your decision--one character paints the Little Sisters as aberrations, one calls for compassion. Of course, the idea of getting more Adam with which to enhance your character is a tempting proposition, but Levine promised that there are other, longer-term rewards for setting the girls free. During my play session, I found myself wrestling with the choice for what must have been several minutes.

"We wanted to make it ambiguous," Levine explained to me. "You've got the one guy saying that they're not really children, then this other person is saying they're children, save them. You're sitting there and they're all telling you different things, and you don't know." I suggested that it seems to be less about doing the right thing, and more about trying to surmise what the right thing might be. "Yes," replied Levine. "No dark side or light side is immediately apparent."

I asked how much range there is to BioShock's gameplay experience, given the two approaches. "It's very different," he said. "The reward system is very different between harvesting and saving. It implies a different route, and there are different gameplay things but also different story elements." He declined to elaborate further, understandably wanting to keep as much as possible about the progression of the game under wraps.

Of course, to be in a position to decide the fate of a Little Sister in the first place will require going through a Big Daddy. BioShock generally aims to allow the player a measure of choice in combat tactics--the powers offer different ways to customize one's character, and the weapons each feature three different types of modifications as well as three different types of ammunition each. A pistol might be modified to hold more ammo or fire more powerful slugs, while a grenade launcher might be modified to direct its grenades' blast away from the player in order to avoid self-harm. That said, most enemies can still frequently be taken head-on if the player so desires, in the style of most first person shooters.

Not so with the Big Daddies. Big Daddies are monstrously tough and incredibly powerful, and require some level of foresight to battle effectively. There was one Big Daddy combat encounter in the hands-on demo, but we were also shown a few different approaches to the same encounter, as played by an Irrational team member named Dean. In one instance, Dean ran into a room with Big Daddies and other assorted enemies. He used the Rage power on the Big Daddy, causing the big guy to go berserk and start attacking the other enemies. This gave Dean a chance to take some well-aimed crossbow shots. Of course, once the Rage wore off, the Big Daddy was rather peeved, but Dean had also set up a perimeter of trip mines around the Big Daddy, which proved to be the foe's undoing. In another instance, Dean used the game's hacking ability (represented by a brief, enjoyable pipe-constructing mini-game) to convert some enemy turrets to do his will. He then used his Incinerate ability to light numerous enemies on fire; when they ran into a pool of water in panic, he zapped the water with lightning, fatally electrocuting all of them.

Continue reading for thoughts on BioShock's atmosphere and storytelling techniques.