The theme is that he was a committed liberal who nevertheless had a unique ability to work with Republicans in order to get legislation passed. The recent-cited example is No Child Left Behind; an example of which I was unaware was the 1996 Kennedy-Kassebaum Act, which enabled workers to retain their health insurance after leaving a job (I assume this is COBRA?).
I saw Kennedy speak in 1994 when I was an intern at the White House. Kevin Dolan was interning for him at the time, and back then my overriding perception of Kennedy was that he stirred up strong emotions (for better or worse) in people.
George Will, who has been emphasizing that our country is too "President-obsessed," says that Kennedy is one of the recent leaders who actually got things done:
In the Senate, as elsewhere, 80 percent of the important work is done by a talented 20 percent. And 95 percent of the work is done off the floor, away from committees, out of sight, where strong convictions leavened by good humor are the currency of accomplishment. There Ted Kennedy, who had the politics of the Boston Irish in his chromosomes, flourished. What Winston Churchill said about Franklin Roosevelt -- that meeting him was like opening a bottle of champagne, and knowing him was like drinking it -- was true of Ted Kennedy, too.