The Legend of Zelda (NES) taught me that there is ALWAYS hidden stuff in game, if you just know where to look. Also some critical thinking under pressure (but really, who uses that?)
The Illusion of Gaia (SNES) unknowingly taught me advanced reading and comprehension, both were required to understand and, by extention, play the game.
Super Bomberman (SNES) multiplayer taught me how to outsmart an AI who knows more about game mechanics than I do.
Parasite Eve (PS1) taught me about Mitochondria and how other cells function in certain ways.
Heroes of Might and Magic 3: Complete (PC) taught me about strategy and not just rolling around a map with one guy who holds me entire army.
World of Warcraft (PC) taught me that neverending games do exist and are pretty fun if you have the time and effort to play.
edit:
rednose1 said:
Orgen Trail taught me everyone, EVERYONE dies from dysentery.
Grandma dies of dysentery, cousin Joe gets hit be EVERY stray bullet fired, and everyone else gets scurvy because no one taught me to YAR HAR PIRATE-- I mean eat oranges and make it k.