Originally released in 1987 in arcades, Double Dragon is an early brawler game credited, in part, for the popularity of the beat-em-up genre during the 1980s and 1990s.
The NES version of Double Dragon is only loosely based on the gameplay and story of the it's arcade counterpart. Instead of the main character, Billy Lee, fighting simultaneously with his brother Jimmy (controlled by a second player), his brother is in fact the end of game bad guy. So although the game offers a 2 player mode, it is played one player at a time.
The player travels through various locations/levels beating up enemies with weapons found on the ground or acquired by knocking said weapons out of the enemies hands. As the player gains experience from killing enemies he is awarded new martial art moves to aid him in fighting enemies - a big change from the arcade version where the player starts with all martial art moves.
The games genre drifts from a scrolling beat'em up to a platform game at certain points where the player must jump over hazards and/or on to moving platforms.
As well as the main game there is also a special version where 1 or 2 players can fight another character. The player(s) must first choose from various character in the game to fight, then the chosen characters are put in a room to fight to the death. The room is approximately two screens wide, but the characters sprites are much bigger than in the normal game mode.