Duke Nukem Forever.

http://duke.a-13.net/

Things that have taken less time than Duke Nukem Forever's Development:
Pop Culture:
The Beatles formed, released every single one of their albums and broke up. During this time they also toured the world several times.
Led Zeppelin released 7 albums, 9 singles, and toured around the world, crossing international borders 27 times (not counting mainland Europe.)
Calvin and Hobbes started in syndication, over the years became widely considered as the best comic strip ever made, then was ended by its creator.
Science & Technology:
The Wright brothers designed and flew the first airplane.
The theory of General Relativity.
The United States' entire program to put a man on the moon, from Kennedy's challenge to the landing.
The complete construction of many monumental buildings and engineering projects. To name a few-
The Empire State Building (Jan 1930 - May 1931)
The Channel Tunnel (Dec 1987 - May 1994)
The Golden Gate Bridge (Jan 1933 - May 1937)
The World Trade Center (Aug 1966 - April 1973)
The digging of the Suez Canal (by hand) took 11 years, from December 1858 to November 1869.
The building of the Titanic took 3 years, from March 1909 to March 1912.
The Hoover Dam was built in 5 years (1931-1936), although it took 9 years on top of that (starting in 1922) for the paperwork.
The tallest structure on Earth, the Burj Dubai, was built in 5 years (2004-2009, technically they're still doing the finishing work).
Wars:
The American War for Independence
The United States Civil War
World War I
The United State's involvement in the Vietnam War.
World War II and the entire Manhattan Project. Yes, even the complete development of the atomic bomb took less time.
Alexander The Great's conquest of Persia took 6 years, from 334BC to 328BC
Julius Caesar's conquest of Gaul took 7 years, from 58 BC to 51BC

This is old.

Not to me

Plus, DNF is cancelled, so it's kind of redundant when you think about it.