The defining characteristic of video games compared to other media is that video games are interactive. It makes sense, therefore, that designers want to incorporate interactivity into the increasingly important, or at least heavily focused on, narrative elements of games. Although players can have a strong impact on the game world, for example by killing the population of a small country, traditionally the player has had limited ability to be involved in the more subtle elements of the narrative. Modern games enable player agency in narrative primarily through presenting the player with decisions. These decisions result in variations to the flow of the game, from world events to character relationships. Most often binary, and never more than a handful of options, these choices make up the branching narrative that most people are familiar with. It is unfortunate therefore that these interactions lack sophistication and often detract from the story more than they enhance it.
There are two major components to plot choices made in video games, namely the narrative and the ethical. The narrative refers to player making a choice based on real or projected aspects of the game world. The question being asked of the player in this case is "how would you like the story to unfold from here?" When making a narrative choice, the player might be expected to consider what they think a character would do, what will lead to the best ending, or simply what's going to be cooler. Although couched in player avatar action, the fundamental aim of such choices is a clear invitation to the player to affect how the story proceeds.
Ethical choices, by comparison, pose the question "what would you do in this situation?". There is no obvious good or bad outcome from a mechanical point of view, and the player often does not have enough information about the protagonist to be able to seriously consider what the character would do. Choices which focus on the ethical component seek to engage the player not as entertainment but rather as a more mentally intense activity.
Broadly speaking, the narrative element of a choice engages the player by highlighting the influence the player has on the world, while the ethical element increases the player's emotional engagement. No matter how ethically or emotionally complex the situation, however, the physical interaction the player has with the game in making the decision is limited by the primitive nature of the controller (discussed in previously here). Take the example of a player given the choice to leave an injured NPC behind to die rather than have them slow down the group. This is presented as an ethical choice, the player will make that choice and then press a button to indicate their decision. In this case, the designer has captured to some degree the turmoil of making the decision, but the player needs only a spit second of resolve to make it. They are not required to do anything to get through the execution of that decision, to tell the NPCs of what will happen. Should designers then not include situations where the execution of a decision cannot be well modelled? Not necessarily, but the execution of a choice should be more difficult than simply pressing a button.
The potential emotional impact of making these decisions in a game is lessened because there is no "what if?". Making a choice is difficult because in part of the knowledge that, once made, the consequences of the choice are irreversible. We may play out a thousand alternative scenarios in our head, but there is no way of verifying their accuracy, let alone ever seeing them actually play out. In a game, if a player wants to find out what would have happened had they made the other choice, they can replay the game, or just find it on YouTube. The alternative scenarios are not hypothetical, they are sitting fully realised on the disc (or more likely in the download directory) and that knowledge diminishes the emotional impact of making ethical choices. It's true that putting the player in control of the situation makes them more invested in the consequences, but the negative effects of knowing that whatever decision is made can be reconsidered and remade are greater. Unfortunately there is no current way around this problem: in order to allow for choice, developers are required to make the content to cover all possible outcomes. Further, if voice acting and performance capture are being used, the number of outcomes that can realistically be covered is very limited.
It is an admirable goal to enable players to have meaningful interactions with characters and events in a game world. However, using simplistic decision mechanics to create branching narratives is a technique which has minimal room for improvement, and one which has been exploited to its limits. Whatever the future is for player agency in video game narrative, it needs to be more than pressing X to decide who lives and dies.