We demonstrate how a first-person shooter (FPS) video game can be made more fun and challenging by replacing the hard-wired behavior of opponents with behaviors evolved via an evolutionary algorithm. Using the opensource FPS game Cube as a platform, we replaced the agents' (opponents) hard-wired behavior with binary DNA supporting a much richer variety of agent responses. Survival-of-the-fittest ensured that only those agents whose DNA allowed them to avoid being killed by the human player would continue on to the next "generation" (game). Mutating the DNA of the survivors provided enough variability in behavior to make the agent's actions unpredictable. Our demo will show how this approach produces an increasingly challenging level of play, more fine-tuned to the skills of an individual human player than the traditional approach using pre-programmed levels of difficulty or simply adding more opponents.