The biggest difference is that the levels are restructured and significantly longer, with stages 5 through 8 being derived from and expanded from areas in the arcade version’s final stage. The plot is altered as well, being set in the year 1987 in the Amazon, rather than 2633 in the Galuga archipelago.
Weapons are slightly different in function and frequency, and the Konami Code makes a famous appearance. The Famicom version has additional graphical effects and between-mission cut-scenes not seen in the NES version.
According to the Japanese promotional materials, Contra is set in the distant future of the year 2633 A.D., where the evil Red Falcon Organization have set a base on the fictional Galuga archipelago near New Zealand in a plot to wipe out humanity.
Two commandos, Bill Rizer and Lance Bean of the Earth Marine Corp’s Contra unit (an elite group of soldiers specializing in guerrilla warfare), are sent to the island to destroy the enemy forces and uncover the true nature of the alien entity controlling them.
The promotional materials for the US arcade version downplays the futuristic setting of the game, with the manual for the later NES and home computer versions changing game’s setting from the future to the present day and the location from Galuga to the Amazon Jungle.