Researching experiential phenomena is a challenging undertaking, given the sheer variety of experiences that are described by gamers and missing a formal taxonomy: flow, immersion, boredom, excitement, challenge, and fun. These informal terms require scientific explanation, which amounts to providing measurable criteria for different experiential states. This paper reports the results of an experimental psychophysiological study investigating different traits of gameplay experience using subjective and objective measures. Participants played three Half-Life 2 game modifications while being measured with electroencephalography, electrocardiography, electromyography, galvanic skin response and eye tracking equipment. In addition, questionnaire responses were collected after each play session. A level designed for combat-oriented flow experience demonstrated measurable high-arousal positive affect emotions. The positive correlation between subjective and objective indicators of gameplay experience shows the great potential of the method presented here for providing real-time emotional profiles of gameplay that may be correlated with self-reported subjective descriptions.