Expert is a modern-day first-person shooter. Taking control of Expert team member Takuya Kudō, the player must clear each floor of terrorists, rescue any hostages, and find the elevator to the next stage. Takuya can choose from multiple weapon loadouts for each stage, and can also find new weapons within the building. The game plays much like Wolfenstein, with simple enemy AI, locked doors, and pickups strewn about each stage. Later stages also introduce environmental hazards such as trapdoors and proximity mines. Progress is saved between stages, and if Takuya is killed by the terrorists, the player must start the current stage over from the beginning.

An unknown terrorist force has taken the high-tech Intelligent Building hostage, along with everyone inside. The elite counter-terrorist team Expert has been called in to neutralize the threat, rescue the hostages, and secure the building.