“When you survey the impact of the Kennedys on American life and politics and policy, he will end up by far being the most significant.”
–Norman Ornstein, political scientist at the American Enterprise Institute
Given his personal problems (Chappaquiddick, drinking, womanizing, a plane crash, failed presidential run), how could Ornstein make such a claim about the brother of John F. and Robert F. Kennedy? The reasons are scattered throughout The New York Times’ well-wrought obit:

Perhaps the last notable example [of bipartisanship] was his work with President George W. Bush to pass No Child Left Behind, the education law pushed by Mr. Bush in 2001.
He also co-sponsored immigration legislation with Senator John McCain, the 2008 Republican presidential nominee….
He led the fight for the 18-year-old vote, the abolition of the draft, deregulation of the airline and trucking industries, and the post-Watergate campaign finance legislation. He was deeply involved in renewals of the Voting Rights Act and the Fair Housing law of 1968.
He helped establish the Occupational Safety and Health Administration.
He built federal support for community health care centers, increased cancer research financing and helped create the Meals on Wheels program…
In one of those bipartisan alliances that were hallmarks of his legislative successes, Mr. Kennedy worked with Senator Bob Dole, Republican of Kansas, to secure passage of the voting rights measure, and Mr. Dole got most of the credit.
Perhaps his greatest success on civil rights came in 1990 with passage of the Americans with Disabilities Act, which required employers and public facilities to make “reasonable accommodation” for the disabled….
In 1997, teaming with Senator Hatch, Mr. Kennedy helped enact a landmark health care program for children in low-income families, a program now known as the State Children’s Health Insurance Program, or S-Chip….
He pushed for increases in the federal minimum wage. He helped win enactment of the Medicare prescription drug benefit, one of the largest expansions of government health aid ever….

This is a partial list. He was also the key legislative player in creating the AmeriCorps law and many others.