The immersive game interfaces which reflect the user's actions to the game in real-time can make the user be immersed in the game. In this paper, we applied the virtual reality (VR) techniques to a first-person shooting (FPS) game, Unreal Tournament 2004, for the enhanced user immersion with making the range of sensible information be widen by using the head-mounted display (HMD) and the 5.1 channel headphone, and also making the interaction between the user and the game system be natural with the head tracker and the data gloves. Additionally, the intelligent game agents are applied to improve the quality of the game contents. The proposed immersive interface was substituted for the traditional interface system represented by a monitor, a keyboard and a mouse. To evaluate the proposed system, we performed the usability test with both the physiological and the psychological measures. Through the experiment, we verified that the proposed system provided better immersive experience to users than the traditional system.