Warning Forever (2003)

A vertical-scrolling shoot-em-up by Hikoza T Ohkubo that consists entirely of boss battles against opponents that are procedurally generated to counter the weaknesses of your fighting style. As you beat each stage, the next boss gets generated with new abilities based on how you destroyed the last one. 

This kind of adaptive play, with systems that react to the player’s actions and generate new content based on them is a powerful approach. It gives the player’s actions inherent meaning, demonstrating an active recognition of the choices that are made. 

This kind of intimate feedback is difficult to create by hand, because choices need to be anticipated by the designer to be recognized, resulting in a relatively limited set of verbs that the game recognizes. But if we create a procedural system that can communicate to the player in its own language, we can create a dialog between the player and the game.