B.I.G. is a action-adventure platformer with gameplay similar to Flashback. A group of fanatics called Apocalypse attacked a convoy carrying nuclear warheads. Their objective is to cause a global nuclear conflict. To prevent the extermination of the human race, the president sends the best agent to the enemy base located in a foreign country, to initiate the process of self-destruction. That is the moment when the player is handed the controls.
Gameplay is much alike mentioned Flashback. There are three levels of difficulty.
The game offers a basic set of movement - run, jump, crouch, crawling, walking ladders, use of weapons. Objects have an impact on visibility. You can use the 8 types of weapons, starting with the sword, ending with the bazooka. There are also several special items such as a magnetic belt (allows to perform long jumps), masking field, accelerator of time, protective energy field.
Player can talk with each neutral character (real voice acting) and record the conversation thanks to voice recorder.
The game contains over a dozen different types of enemies - humans and robots, and some specific equipment, like switches, computer terminals, elevators, magnetic cards, teleportation platform.