Because I say it is. (Nah, jk.) It revolutionized not just Zelda games, but general gaming in some ways. The dungeons were deep, even by today's standards. The gameplay was top notch for its time, and is still pretty decent today. Ocarina of Time was the first shot at Zelda 3D, and it basically perfected it. Ocarina of Time is one of those games that's still great today. It's not just one of those games that was great for its time (like Sonic Adventure). It's the best Zelda game to date. We'll have to see how it holds up against Skyward Sword, though.