The original "Metal Gear" was a commercial success for its release on the NES, and Konami decided to create a sequel to the game, "Snake's Revenge," without the involvement of Kojima. When Kojima was riding on the Tokyo transit system, he was told about "Snake's Revenge" by a colleague working on the project, who asked him to make a new Snake game of his own. As a result, Kojima began work on his own sequel, ', and the two were both released in 1990. Kojima's game would not be released overseas in North America and Europe until its inclusion in ' (2006). "Metal Gear 2: Solid Snake" was a commercial success. The game has received positive reviews from retro-reviewers. IGN notes that "Metal Gear 2" introduced stealth mechanics such as making noise to attract guards, crouching and crawling on the ground, disarming mines, and enemies having view cones.