The Game Genie is actually a fascinating piece of hardware/software, and there are many great tales like this one associated with it. Also of significance is its cousin, the Game Shark, which came a bit later.
I never really got the hang of asm myself, though... I should probably give writing some GB software a crack at some point. I might actually learn it if there's a use.
Game hacking is pretty fun. One useful(?) task is to search for unused stuff in games and document it at <http://tcrf.net >. For example, I learned 6502 assembly and NES MMC3 codes to write a level map dumper for M.C. Kids and its prototype, which lead to a full comparison of how the levels changed during the game's development process <https://tcrf.net/Proto:M.C._Kids#Level_Changes >. It was a really fun learning experience.
I never really got the hang of asm myself, though... I should probably give writing some GB software a crack at some point. I might actually learn it if there's a use.