It forever changed: Everything about 3D exploration in gaming. Go on, name any game off the top of your head - chances are its actual mechanics were directly influenced by the fifth (and some say still best) Zelda title in history, not to mention the huge amount of artists, programmers and industry figureheads that grew up playing this and were inspired to go off and make their own gorgeous worlds to escape into. Little things like fast-travelling around a map - something you might have got your first taste of in Vice City when you hopped inside a taxi - originated in Ocarina, and if that wasn't enough, you combine that with the beauty of Z-targetting (moving towards and away from an opponent) which back in 1998 was mind-blowing. Suddenly you had a very immersive open-world experience that was immediately engaging, had a compelling fairytale-esque narrative, a meaty combat system to back it up and production values everywhere that mattered to top it all off.
