|"Farewell remorse; all good to me is lost."|
My favorite tabletop RPG alignment system is the Path mechanic in Vampire: the Masquerade. By default, PCs (who are all vampires) follow the 'Path of Humanity', essentially a simulation of secular humanist morality on a scale from zero to 10. Each level has a set of behavioral standards, the violation of which triggers a roll that determines whether the character feels remorse for the action, thus retaining his Humanity, or rationalizes the action and drops one level on the Path.
This mechanic seems clunky, but I have found it surprisingly useful and intuitive in the context of the game. It has an admirable balance of crunch and fluff, providing system incentives both for maintaining a high Humanity score and for letting it slide, just a little. Even more, the game contains several other Paths to which characters can 'convert' if they reject Humanity, including ones that glorify that which most humans conventionally regard as 'evil'.
Many video games have linear alignment systems. Star Wars games, such as the Knights of the Old Republic and Jedi Knight series, use the Light Side/Dark Side system as portrayed in the films. The Karma systems in the inFamous and Fallout series both measure morality on a Good/Evil axis, and adjust the way NPCs interact with the PC accordingly. A common problem with these single-axis mechanics is that they often yield rewards only at the extremes, which can discourage roleplaying in favor of powergaming the alignment system.
The most interesting and nuanced alignment system I have encountered in a video game is Reputation in the Mass Effect series, which grants Paragon or Renegade points for dialogue choices as well as other actions. It looks like a single-axis Good/Evil system on the surface, but in fact Paragon and Renegade are closer (though not equivalent) to Lawful and Chaotic. Furthermore, they are measured on completely separate scales. So the player can gain both Paragon and Renegade points in the course of a single encounter without one canceling out the other. High scores on these axes unlocks special actions that can affect the game in fairly dramatic ways.
I find, sometimes to my own disappointment, that I gravitate toward playing 'good' PCs. I derive a great deal of satisfaction from portraying a well-developed villain or anti-hero when I game master, yet have little interest in such characters as a player--this includes video games. I have occasionally made 'bad' characters in games like Jedi Knight or inFamous just so I can go on a rampage, but lose interest in them fairly quickly. Unless I make a conscious effort--and sometimes even when I do--I end up playing goody two-shoes characters. This probably explains, at least in part, why I have so much interest in alignment mechanics that break the Good/Evil mold.