Game Plotline ideas:

Heaven & Hell

Part 1: Sacrifice

General premise: It's time to put an end to the suffering of the world.
Objective: Hero ("Satan"?) to take on the burden of all that suffering.
Endgame: The creation of hell, the prison of suffering.

Part 2: Suffering

General premise: It's time to put an end to the suffering of the hero.
Objective: Develop the solution to suffering itself.
Endgame: The creation of heaven, the solution to suffering.

Part 3: Insanity

General premise: Hero has gone insane from the suffering, and believes that ending suffering will end his existence.
Objective: Save the hero from his burden, to end the suffering of hell.
Endgame: The removal of the leader of hell, but not the end of hell (would necessitate the hero's obliteration?)

Part 4: War

Objective: Destroy hell, and relieve the world of it's burden.
Endgame: The destruction of hell.