The success of “The Sims” is something of a mystery to most gamers.

Somehow, a game that simulates sleeping, eating, going to work, and making friends became the most successful PC gaming franchise of all time, with sales topping 100 million units before the newest version — “The Sims 3” — was even released. Since the first “Sims” in 2000, some permutation or add-on of the game has never been off the best-selling charts.

“The Sims” grew out of “Sim -City,” the landmark urban-planning simulator created by designer Will Wright. Over time, the franchise took on the simulation of different systems — cities, ant farms, high-rise buildings, roller coasters, driving, and on and on.

The game brought the entire concept down to the detail of an individual life. You create a person, and then nudge them through their days by having them perform routine tasks, buy stuff, get a job, go to the bathroom, and redecorate the house.

I’ll make this as succinct as possible for the men in the audience: A central part of “The Sims” gameplay involves perusing wallpaper swatches and matching them with carpet swatches in order to redecorate your home. Most men I know wouldn’t call this “entertainment.” They’d call it “penitential.”

This probably explains why the game skews heavily towards a female audience. The gender split among “Sims” gamers is about 60% to 40% in favor of women, which is roughly twice the average number of female gamers.

“The Sims 3” is the most recent entry in the series, and it takes all of the standard gameplay elements to the next logical step, with sometimes disturbing results. The game world has expanded beyond the boundaries of the household and into an entire continuous virtual neighborhood, with no gaps or load times as you go from place to place.

There are places to work, play, learn, improve yourself, and meet others, and no barriers to exploring it all at will.

The creation of a “sim” is completely in your hands, as you twiddle an astounding array of options for physical features and personality traits. Sims can now have up to five “social traits” which affect the way they respond in certain situations. These are things like “family-minded,” “evil,” “bookworm,” “mooch” or “excitable” that help shape the actual character of the simulation and the way other characters respond to him or her.

Sims also get “lifetime wishes,” which are goals such as “become a superstar athlete” or “chess legend.” Other wishes might be as simple as “read three books” or “learn how to cook.”

When a wish is achieved, the character earns points that can be spent on perks like a teleporter or other improvements. Sims can start as kids, get older, marry, begin a family, have their own kids, advance in their career, and even die. (Some of these options, such as aging and death, can be turned off.)

“The Sims” titles have always been an “open system,” meaning that the designers create tools with few restrictions, allowing people to use them in often unforeseen ways.

Indeed, creator Will Wright often refers to his projects as “software toys” rather than “games” in the orthodox sense.

What the designers allow, however, may not be something parents want younger kids to experience.

Sexuality and homosexuality have long been part of “The Sims” experience, with couples flirting, kissing, having sexual relations, and even forming “unions” regardless of gender.

With “The Sims 3,” full “gay marriage” has finally arrived, with no distinction at all between actual marriages and same-sex “marriages.” Two men or two women can have a complete wedding, set up a household, and have children.

Some of the sexual elements will be well outside the comfort zone of many parents. Nothing explicit is shown, but the presence of these elements should have been enough to earn “The Sims 3” a M-rating (“Mature”). As it is, it gets away with a T-rating (“Teen”).

Sex is remarkably casual in the world of “The Sims 3,” and sleeping with your boss to get a promotion is even a gameplay option. In fact, dishonorable behavior is a perfectly fine choice since the game world is intentionally void of moral limits, although murder, smoking and drugs do not appear.

The designers are creating not so much a game or a narrative, but an environment and set of tools for people to create their own narrative. The assumption is that the gamer brings his or her moral values to the experience.

People can be who they want to be — unless, of course, you want to be a person of faith. Religion and belief still do not figure into the game at all. “The Sims 3” offers perhaps the only town in America without a single church or synagogue.

The game does, in fact, have a single throbbing core value: rampant materialism. It is the pulse at the heart of all “Sims” games. You’re not so much creating a life as you are creating a life upon which to hang lots and lots of stuff. You’re nurturing a tiny consumer.

“The Sims 3” is completely wired into the Internet, allowing you to buy (with real cash) more furniture, cars, clothes and stuff to add to “The Sims 3.” Then, you have to play the game until your characters have enough money to buy the stuff (with sim cash) in the game world.

It’s a world full of routine, mundane and often frustrating tasks where God is absent, love is simulated, and the sole gauge of success is material prosperity.

I’ll take a mindless first-person shooter over that any day.

Thomas L. McDonald is

editor-at-large of Games magazine

and a catechist in the Diocese of Trenton, New Jersey.