Defender

Defender was the most complex shooter of the 2600 era: a map scrolling in both directions, aliens kidnapping humans and transforming them into mutants, and a miniature radar monitoring the battlefield. The arcade cabinet had five buttons and a joystick — the 2600 version condensed everything into a joystick and button with surprising ingenuity. The responsibility toward the tiny humans to save created rare emotional tension for the era. Defender sold well but was notoriously difficult — few reached the second level without weeks of practice.