I find it interesting that the Gameboy was the real genesis of not one, but two genuine pop-culture phenomenons. First, there is Tetris, which although had been released in the arcade and on the personal computers of its day, really emerged as a phenomenon with its release for the Gameboy. Not only did the game almost single-handedly ensure the survival of the Gameboy and the viability of handheld gaming, it also got people who never played a videogame before to try them. Many, many console and handheld versions followed, but this simple pack-in was almost certainly the wisest pack-in Nintendo did since the original Super Mario Bros. with the NES.
Towards the end of the Gameboy's (monochrome's) life, the Pokemon games were released for the system, giving it a new lease on life. Pokemon, unlike Tetris, actually started its life as a pair Gameboy games. Unlike Tetris, Pokemon was able to cross over from videogames into a highly successful anime series and collectible card game. It is a staple of toy lines. Its immediate sequels helped ensure the Gameboy Color's success.
Most consoles would be happy if they could establish one marketing juggernaut, a game that truly stands out and transcends the medium. The Gameboy had more than most, not bad for the little monochrome system.