Just a few minutes into that underwater art-deco classic Bioshock, the gamer is presented with a stark choice—kill the creepy young girls known as “Little Sisters”  or try to save them. Both decisions come with benefits and consequences, but seeing as how I played Bioshock with my wife, there was no choice. I was not allowed to commit sororicide.

But she was away on business when I fired up Fallout 3, a game-of-the-year contender from Bethesda, the makers of Oblivion, which similarly allows you to play as good or evil. But while Bioshock’s moral dilemma didn’t have much impact on the game, aside from a slightly altered ending, Fallout’s karma system has more wide-reaching implications.

Not to mention that deciding between harvesting or rescuing zombie tweens is somewhat less disturbing than the choice Fallout presents us a few hours in—do you nuke an entire town just to make a quick buck?

To backtrack, Fallout 3 is the now-gen sequel to a PC classic from a decade past. Set in and around a post-apocalyptic Washington, DC, it takes place in a retro-future as imagined by the denizens of the 1950s. Due to a nuclear holocaust, I’ve grown up in an underground vault which I’ve left, for the first time, in search of my missing father.

But he apparently failed to instill in me a moral compass because I’ve been committing bad deeds all across the wastelands. Most notably blowing the holy hell out of the trading-post town of Megaton (named after an unexploded nuke that sits in the heart of the town) despite all the people I’d met inside. Though to be honest, once I decided to go through with exploding the bomb—even though the sheriff offered me a reward to disarm it—I methodically went around killing and robbing much of the townsfolk.

But once I was up on Teapenny Tower, watching the mushroom cloud form over the former town of Megaton, I started to feel a little, well, icky. That’s the thing about role-playing games. When you’re shooting at cops in Grand Theft Auto 4, it’s not really you—it’s Nico Bellic. There’s no similar distancing in Fallout 3. Or Fable 2, for that matter, another just-released RPG which evolves based on your actions, offering branching storylines and character interactions (though in Fable, the more evil you get, and the uglier your avatar becomes).

In both games, your good or evil actions affect how the non-player characters react to you. It’s a neat way of making every gamer’s experience unique, but it also adds some much-needed greyscale morality to an often black or white medium which generally lets you get away scot-free with killing countless “enemies.”

So that kid wandering the wastelands who asked if I could fight off the mutant ants attacking his town. Maybe I’ll help him out. I could probably use the karma.