Featured in many tournament winning decks, Gordian Blade is one of the most powerful breakers in the game. It has the combination that everyone loves: 1, 1 to pump, 1 to break. It's reasonably efficient for early game (e.g. Enigma), high subroutine (e.g. Merlin), and high strength (e.g. Tollbooth) Code Gates.
The Blade is not as weak as ZU.13 Key Master, not as expensive as Torch, doesn't require stealth (unlike Refractor), can be pumped to infinity (unlike Yog.0), and is not limited to a single server (unlike Cyber-Cypher). Like all great hacking tools, it is flexible, efficient, and elegant. If you are only putting one Decoder in your deck, it is a solid choice.
It is also a subtle reference to a famous Greek Legend. For those of you who are unfamilar:
Long ago, an oracle decreed that the next man to enter the Phrygian capital (modern Turkey) should become king. Gordias, a peasant, drove into town on an ox-cart, and was declared the ruler. Out of gratitude, his son dedicated the ox-cart to Zeus, and tied it to a post in the palace with an intricate knot that had no exposed ends ("GORDIAN Knot"). The cart stood unmoved for generations. It was, in fact, still there when Alexander the Great arrived. Alexander attempted to untie the knot, but could not find the ends. Instead, he sliced it in half with a stroke of his sword-er, wait, I mean, BLADE. Once Alexander moved the cart, an oracle further prophesied that the one to untie the knot would become king of Asia (... and win a Fantasy Flight game mat).