Short answers, pulled from the story.
Metal Gear 2: Solid Snake is a 1990 action-adventure stealth game that Konami developed and published for the MSX2. It is the second mainline entry in the Metal Gear series and a direct sequel to the original Metal Gear from 1987.
Hideo Kojima, creator of the Metal Gear series, wrote and designed Metal Gear 2: Solid Snake himself. He conceived it partly in response to Snake's Revenge, a separate NES sequel Konami was developing at the same time for North America and Europe.
Konami released Metal Gear 2: Solid Snake in Japan on the 20th of July 1990 for the MSX2. It did not receive an international release with full English localization until 2006, as part of Metal Gear Solid 3: Subsistence.
The game sends Solid Snake into Zanzibar Land, a Central Asian territory, on Christmas Eve of 1999 to rescue kidnapped scientist Dr. Kio Marv and stop a nuclear-armed successor to Metal Gear called Metal Gear D. Along the way Snake discovers that his former commander Big Boss survived their earlier fight and now leads Zanzibar Land.
Metal Gear 2: Solid Snake let enemy guards patrol across multiple screens instead of staying fixed in one, widened their field of vision to 45 degrees, and gave them the ability to hear sounds such as gunshots and footsteps. It also added kneeling and crawling, a 3x3 radar grid, and a revamped context-sensitive transceiver system.
GameSpy's Paul Soth wrote that Metal Gear 2: Solid Snake surpassed its predecessor in every way and called it one of the best 8 bit games ever made. Game Informer was more critical, giving it 7 out of 10 and calling its backtracking and keycard-based design too repetitive.