Games are a flexible medium, capable of everything from the mildest momentary diversion, to complex simulations of reality, to profound narratives that blend storytelling with interactive elements.

All too rarely, a game like “BioShock” comes along to show us that the medium is capable of presenting momentous issues in a complex and intelligent way. Although it was released last year for the PC and Xbox 360, its debut for the PlayStation 3 (complete with some new puzzles) gives us a chance to explore a profound interactive experience.

Narrative complexity, character development, and even thematic depth are fairly common coin in modern game design, but “BioShock” takes things further, probing issues of morality, bioethics and the nature of the self.

The setting is striking: an underwater libertarian-objectivist dystopia where the cult of selfishness drove the population to addiction and madness. As you explore the levels, you perform the standard actions of any first-person shooter (collect weapons and kill monsters), but you also solve the mystery of this strange city.

The story begins in 1960, as a plane crashes into the middle of the ocean, leaving you as the only survivor. Swimming through the burning wreckage, you encounter a strange lighthouse rising out of the deep. Inside, a bathysphere takes you to the bottom of the ocean, where a megalomaniacal visionary named Andrew Ryan has built a city called Rapture.

Ryan is a radical objectivist millionaire who tried to create an anarcho-capitalist utopia. He’s Ayn Rand via Charles Foster Kane, with a bit of Howard Hughes tossed in for good measure.

Rapture is his monument to narcissism. Its soaring architecture and burnished brass seem like set designs by Albert Speer for an art deco-production of Atlas Shrugged.

These are not mere monuments to the ego of one man. Although Ryan’s cult of personality is complete and smothering, Rapture is designed to create an entire city full of narcissists. The worship of self is central, as Ryan makes clear in one of his many pronouncements:

“Is a man not entitled to the sweat of his brow? No, says the man in Washington. It belongs to the poor. No, says the man in the Vatican. It belongs to God. No, says the man in Moscow. It belongs to everyone. I rejected those answers. Instead, I chose something different. I chose the impossible. I chose … Rapture.”

In Ryan’s philosophy (as in Ayn Rand’s), people should think only of themselves. Rapture was created so that scientists would be able to conduct research free of the ethical constraints of civilization, so artists would not be bound by outdated moral codes, so that people could explore their true potential no matter the cost.

As you’d expect from such a libertarian wonderland untethered from morality or restraint, it doesn’t take long for Rapture to descend into utter chaos.

As the game begins, the city is already a leaking husk overrun by genetic mutants as various factions fight for power. The story of Rapture’s collapse emerges piecemeal through messages and recordings collected in the course of exploration.

Rapture’s collapse is an object lesson in what happens when bioethics break down. The city is undone by genetic tampering as people attempt to turn themselves into gods with gene-modifying drugs. God’s work is imperfect, people are told, so science must step in to improve it.

Ryan sees Rapture as a new Eden. Indeed, two of the game play elements are “ADAM,” a mutagen (a physical or chemical agent) that allows people to modify their genetic structure to enhance certain powers, and “EVE,” the fuel for these genetic mutations.

In order to get through Rapture, your character needs to become one of these mutants — without sinking too far into madness. It’s a dangerous balance, and in the end only love is able to bring you back, if you choose the path of love as you play.

As you need more and more of these drugs to progress through the game, you’re forced to make moral choices. One type of “monster” in the game looks like a little girl. These monsters were created as little more than a source of raw materials to be exploited by a scientist. But the scientist didn’t count on their humanity, or her own.

As she says at one point: “I look at genes all day long, and never do I see the blueprint of sin. … These children I brutalized have awoken something inside that for most is beautiful and natural, but in me, is an abomination ... my maternal instinct.”

Life wins out, however. The doctor turns on Ryan in order to protect these little girls, and you are forced to make a choice: Follow Ryan and simply destroy the girls, or follow the doctor, and save them.

The game makes it pretty clear which route is preferred, with two endings based upon the choices you’ve made.

Make no mistake: This is a violent, M-rated (for violence, drugs, language and sexual themes), adults-only action game, and fans of the genre know what to expect. It’s also brilliantly written and, at times, profound.

“BioShock” shows us a stark picture of what libertarianism and objectivism would look like in the real world.

Unfettered individualism does not lead to an objectivist utopia. It leads simply to Rapture and the hell of a society filled with narcissists trying to make themselves gods.

“BioShock” puts you in the middle — and forces you to choose a side.

It’s the kind of choice a radical objectivist like Ryan would believe is irrelevant to society, but it has an absolutely central effect on how the game plays out, leaving us with a very clear message about right and wrong and the place of the individual in society.

Thomas L. McDonald is

editor-at-large of Games magazine and a catechist in the Diocese of Trenton, New Jersey.