"Mega Man 4 (ロックマン 4 新たなる野望!!, Rokkuman Fō Arata Naru Yabō!!?, Rockman 4: A New Ambition!!) is a video game developed by Capcom for the Nintendo Entertainment System. It is the fourth game in the original Mega Man series and was originally released in Japan on December 6, 1991. The game was localized in North America the following January and in Europe on December 14, 1992. The game also saw later re-releases on the Japanese PlayStation and mobile phones, the North American Mega Man Anniversary Collection, and the Wii Virtual Console. After the third defeat and supposed death of Dr. Wily, the Earth comes under threat from a mysterious scientist named Dr. Cossack and his eight Robot Masters. Fearing the worst, Dr. Light sends Mega Man to save the world once again.
Mega Man 4 carries on the same action and platforming gameplay as the first three Mega Man games. One notable added feature is the "Mega Buster", an upgraded arm cannon that lets the player charge a shot for a much more powerful blast. Though Mega Man 4 received positive critical reviews during its early 1990s release, the game is widely considered today to represent a downward shift in the overall quality of the series, particularly for its immediate sequels. The Mega Buster itself has been considered an overused mechanic, even by series contributor Keiji Inafune."
Source: Wikipedia, "Mega_Man_4," available under the CC-BY-SA License.