Schneider, E. F., Lang, A., Shin, M., & Bradley, S. D. (2004) Death with a story: How story impacts emotional, motivational, and physiological responses to first-person shooter video games. Human Communication Research, 30, 361-375.

Abstract
This study investigates how game playing experience changes when a story is added to a first-person shooter game. Dependent variables include identification, presence, emotional experiences and motivations. When story was present, game players felt greater identification, sense of presence, and physiological arousal. The presence of story did not affect self-reported arousal or dominance. This study clearly demonstrates that story is something that video game players enjoy; it helps involve them in the game play, makes them feel more immersed in the virtual environment, and keeps them aroused. The greater character identification may be especially worrisome, as past research has shown that justified media violence disinhibits actual aggression on the part of the audience.