For anti-WWE alarmists the date June 27, 2002, was the beginning of the end. If you didn't know it from the mass amounts of rantings online, it was the day the first lines of Skynet code were written.
April 3, 2005—Judgment Day. John Cena wins the WWE Championship at Wrestlemania 21.
Some like to call a small brief period in time from some where in 2002 to 2007—The Ruthless Aggression era.
2002 to 2005 is probably more in tune with the "ruthless aggression" philosophy. Either way, I like to call these three years—When WWE really sucked.
Today and for the last five years the WWE has been much more exciting than it was for the brief few years in the early part of this decade.
At the time the WWE suffered dramatically—poor story lines, poor wrestling, poor pushes, and even poorer character development.
John Cena winning the World Championship and becoming the iconic brand he is today sparked a change in the WWE.
In the years, that followed Edge became the Rated R Superstar—the two would engage in the epic back-and-forth war for much of the remaining decade, cementing Edge was the Superstar he is today.
Randy Orton would become the incredible anti-hero character. Something only possible with the establishment of the clean-cut, all round good guy—John Cena.
He made ECW One Night Stand the show it was—something no other man in WWE could.
The entire NXT roster owes John Cena for beginning their careers. Again not one man in the WWE could deliver what John Cena did that fateful night.
The reaction to the angle proving John Cena is the only true franchise player and the true talent that most make out he isn't.
John Cena as it all—charisma, loads and loads of it. Wrestling skill—he may not do much, but he does it smoothly, safely and most importantly has a better mind for psychology and story telling than more than most of guys to win the WWE Championship.
In summary—size, power, charisma, likability & marketability. Every thing that makes or breaks a WWE Superstar's career.
Christ, when he's got it all... he's just too easy to hate and we're reading from the book of Lance Storm, John Cena is just too easy to blame for everything that's wrong with WWE.