Nintendo certainly played their cards right with the Game Boy, from the hardware (understanding battery life over screen quality early on) to the pack-in (Tetris being quite an International business affair) and the marketing for it all.
For the most part, this is the device that made me a day one buyer of Nintendo hardware for a couple of decades (Gamecube being my last Nintendo day one purchase - the Wii just went weird for me).
Just shows Nintendo is a safe bet in gaming.