Most video games have plot-themes so thin that the average action B-movie (like the Sci-Fi Channel's Ice Spiders) looks like Hamlet by comparison. It's so uncommon for a video game to have a plot-theme deeper than, "Kill all the bad guys," that when one does come along it immediately grabs my attention. Dreamfall: The Longest Journey is just such a rarity.
Its theme is the role of Purpose in life, and the plot-theme is how the integrity of one's purpose affects outcomes for oneself and the world. To show how the author integrates this theme into the story, I'll have to reveal some elements of the story, including ending details.
There are three main characters. One chooses her purpose according to her nature, one chooses out of guilt, and the third chooses to let others dictate his to him, out of blind faith.
The first, Zoë Castillo, begins in a purposeless funk, and through acting in accordance with her values discovers what she is meant to do. At the end she has succeeded in her newfound goals and gained inner peace. Though she dies at the end, it is an acceptable death.
The second, April Ryan, having fulfilled her purpose in the previous story, chooses her purpose from misplaced guilt over the consequences of her prior actions. This has made her bitter and cynical, and in the end following that purpose brings disaster both to herself and to those she sought to help.
The third, the Apostle of the Goddess, lets his faith guide him and takes as his purpose following the orders of his superiors in the theocracy. This leads him into actions he believes are righteous but will later offend his sense of justice. When the contradictions between his superiors' claims and what he witnesses first-hand become too obvious to ignore, he is troubled and begins to question his purpose - which gets him arrested for treason.
So the author shows us that choosing a purpose integrated with one's values (friendship, knowledge, justice) leads to inner peace and possible success while choosing one in conflict with those values leads to bitterness, cynicism, doubt, failure and disaster.