The Legend of Zelda the classic Nintendo franchise next to Mario produced by Shigeru Miyamoto.
The first Zelda game, "The Legend of Zelda" originally came out 1986 on the NES. This was the game that brought console gaming to a whole new level of complexity. Up until that point people were used to play simple games such as jump and runs on their consoles, and usually having to beat them in one sitting.
Just by taking note of the fact that "The Legend of Zelda", being sold in a golden cartridge, was the first (and only?) NES game to include a battery for saving your progress you can get a sense of the amount of hours of gameplay you can get out of this game.
The player takes control of Link, a young boy in a green robe.
The game gives you no tutorial whatsoever, you start in a valley without any goal or instructions. Soon you will get your first sword handed to you, giving you the tool to progress further and onto the first dungeon you will eventually come by.
In each dungeon you'll find one new weapon or tool and heart container, guarded by the dungeon's boss. You don't necessarily need to beat the dungeon's bosses, but the extra heart containers will come in handy the further you progress in the game.
You do however need the weapon/tool to make your way to the next dungeon. It may bombs that let you destroy a rock blocking a passage or a raft, helping you to get over a lake.
This mechanic (which was later copied in the Metroid series, also by Nintendo) allows each player to play at his own pace. The game doesn't rely on scripted events to let him continue and it brings up a great open world feeling.
This formula was kept in every game of the franchise to be released since then (except for Zelda 2), no matter if it was a 2D or 3D game.
If you haven't already played a Zelda game (I bet by now everybody and their grandma has) you should crawl out from under your rock and give the franchise a try.
You don't have to start with the first one (which is also by far the hardest (except for maybe Zelda 2)) as the franchise offers no continuos story anyway.
If you want to start with a 2D Zelda try either "The Legend of Zelda: A Link to the Past" on the NES or "The Legend of Zelda: Link's Awakening" on the Game Boy (which was by the way my first Zelda game).
If you'd rather try a 3D Zelda go give "The Legend of Zelda: Ocarina of Time" or "The Legend of Zelda: The Wind Waker" a try.
I don't think the other installments are bad, but it's just my personal recommendation.