This is incredibly shocking, for a couple of reasons, most notably that Russert was probably the most larger-than-life person in all of political media.
He effectively had "called" the Democratic nominating process for Barack Obama the night of the Indiana-NC primaries, and it could be argued that it was the beginning of the end of the beginning. He seemed to be particularly energized by this election year.
His connection to sports was obvious (especially on Meet the Press) and he was a passionate fan, especially of his beloved Buffalo Bills. Whenever I was at a Wizards game, he seemed to be there. He was on the Board of Directors of the Baseball Hall of Fame. (Here is a relevant sports-focused Q&A with him from an old Page 2 feature.)
The timing seems remarkably cruel (as if the timing of death is ever anything but), given that it is Father's Day weekend and Russert's best work probably came when writing about his father, "Big Russ and Me."
Condolences to his family, friends and fans.