Video games are almost always based on the premise that the character you control is the good guy. Even in games like those in the Grand Theft Auto series that have players piloting an individual who is, both in plot missions and in general gameplay, a mass murderer, the game itself is set in a world populated almost exclusively by equally bad people. This has come to be a huge problem in more complex, story-driven games as of late. When given the choice to roleplay a hero or a villain, do games actually make that choice worthwhile?
Let's take a look at the place where this problem comes up most frequently: Roleplaying games with dialogue trees. A holdover from the era of text adventures, dialogue trees allow players to affect a personality of their choosing on the main character of a game, ostensibly being given the chance to be a virtuous good guy, an unrepentant jerk, or something in between. Except it usually doesn't work out this way. Even though the illusion of choice is there, most games are still overwhelmingly designed with heroic dispositions in mind.
Consider just about every game published by Bioware in the past decade. A lot of these are great games, like Star Wars: Knights of the Old Republic and Mass Effect, but they struggle to offer a worthwhile experience for players who would rather be a heel for a while. The limitations are built right into the mechanics. Supporting characters understandably don't like being insulted, ordered around and generally treated poorly, but those are the dialogue options available for the "Dark Side" and "Renegade" options in the trees. In order to unlock new missions and learn more about these characters, the player has no choice but to be nice to them.
This content limitation is a huge problem. Players should not be penalized for character consistency just because the character is consistently mean or inconsiderate. But this seems to be the standard approach to game design these days.
For a prime example, look no further than Fallout 3. The Bethesda Fallout games offer a lot more options to evil-leaning protagonists, but they still shrink the experience down as a result. In an iconic moment in Fallout 3, players are given the option of detonating a nuclear bomb situated in the middle of a town in exchange for a lot of money and a room in the nicest, safest place in the entire game world. But this, understandably, removes a worthwhile resource from the game and a whole slew of missions. For doing the selfish, evil thing, players are essentially given less game to play.
Designers are going to have to work around this problem eventually. It's true that it's hard to come up with compelling reasons for a selfish, inconsiderate protagonist to help anybody with anything, and it's also true that creating two distinct but equal streams of content, one for the hero protagonists and one for the villain protagonists, would be expensive and difficult. But if games that already have elaborate moral structures like dialogue trees and story-altering decision points are ever going to be truly engaging, they're going to have to let players get as much enjoyment out of roleplaying a monster as they get from being a paragon.