Lawful Good or Neutral Evil? Open Palm or Closed Fist? Such questions were inconceivable in gaming's early days. Rogue didn't care if you styled yourself a noble hero, and the classic Gold Box games wouldn't let you be much else. The first major North American computer roleplaying game to seriously consider any form of player alignment, Ultima IV, demanded the player conform to the game's eight virtues. When your choices are limited to honesty, compassion, humility and the like, it's hard to be, well, evil.
But just how far have we come in the past two decades?
Ultima's Virtues, Fallout's Karma and Reputation, Fable's point system, Jade Empire's Paths and other player alignment systems owe an enormous debt to the original alignment system - the one introduced by Gary Gygax and Dave Arneson in Dungeons & Dragons. Originally just a single axis with three points (Law, Neutrality, Chaos), Advanced Dungeons & Dragons expanded it into the two-axis, nine-point Good-Evil/Law-Chaos framework used most famously in the digital realm by BioWare and Black Isle.
On the surface, the "Gygax model" seems to offer more flexibility for player alignment systems than its most common CRPG alternative - single-axis Good/Evil models. Both typically associate Good with altruism and Evil with self-interest, but the Gygax model offers the additional axis of Law and Chaos, corresponding roughly to authoritarianism and libertarianism. This allows games implementing the Gygax model to assign alignment labels to actions that wouldn't be clear-cut in a single-axis Good/Evil model.
For example, is rescuing your convicted friend from prison a Good act if she is actually guilty? This is awkward to address in a single-axis framework, but in a game implementing the Gygax model it would shift the player's alignment in the Chaotic direction. Regardless of motive, it is a clear defiance of law. What about a player who advocates changing the law, then? Civil disobedience is certainly Chaotic, but legitimate legal protest doesn't exactly conform to the Gygax model's ideal of Lawful, which entails conforming to the will of a sovereign.
The Gygax model's weaknesses stem from its origin in D&D, which began life as a glorified tabletop miniature wargame. Players in D&D needed to be able to choose from balanced classes with defined roles, and the player group needed a common goal. The alignment system restricted the actions of players choosing to play certain character classes, which compensated for the special abilities of those classes. The prominence of altruism and the overall emphasis on heroism at the Good end of the alignment spectrum helped foster player cooperation. To make it work, Good and Evil were precisely defined, tossing aside more than two millennia of philosophy, which made it difficult for any game implementing the model to ask meaningful questions about the nature of Good or Evil.
Typically, the Gygax model is codified in a CRPG by assigning alignment weights to various actions and dialogue choices. A player wishing to be Good should choose the most polite dialogue options and make sure to commit acts of kindness on a regular basis; a player wishing to be Evil can feel free to fling all manner of insults at non-player characters and then rob them blind. Neutrality is awkward - rather than remaining Neutral by striving to chart a course along the middle ground between Good and Evil and/or Law and Chaos, players remain Neutral by perpetrating an equal weighting of Good and Evil acts. There's no way to differentiate a shift toward Neutrality from a shift toward Good, Evil, Law or Chaos in the Gygax model.