The game, Legend of Zelda - Ocarina of Time - is one of the first 3d RPGs. It was revolutionary in the sense that the user has a very high degree of freedom in controlling the main character. Originally designed for the Nintendo 64, this game uses a joystick mounted on the Nintendo's controller. The user is free to target objects in the world via moving the targeting crosshair using the joystick.
This game is also known for the great deal of freedom involved with finding objects, secret passages, and extra information. All of this exploration is somewhat analogous to locating and following links in hypertext pages. The game and its rooms are arranged in a web, where the user is free to talk to any non-player characters, and wander around completing goals.
Due to the fashion in which earlier Zelda games implement fighting, this game uses the same lock-on system used for targeting people to engage in combat. Used in every 3D Zelda game to date, it was quite a revolutionary feature when it was new.