Fallen Angel is a side-scrolling action game where players control a divine warrior tasked with dismantling a global drug syndicate. Starting in London's underground rail system, players navigate through multiple train stations, fighting thugs and bosses using hand-to-hand combat and occasional weapon pickups. Each level requires finding a plane ticket to progress and defeating a local crime boss, with players free to explore stations in any order via the subway system. The game's nonlinear structure allows players to tackle objectives as they choose while progressing through an international criminal underworld.