One unique feature of the presidential election of 2000 between george w. bush and al gore is that (1) the supreme court played an important role in the final outcome (2) no third-party candidate was on the ballot (3) both candidates had previously served as vice president (4) the electoral votes in florida were divided between the candidates

The Unique feature was that even long after the election, it was not clear who had won, and the crucial decision depended on the re-count of votes in Florida.

This re-count was stopped by the Supreme court and as a result, George Bush won (based on the previously announced number of votes)

So the answer is:
 the Supreme Court played an important role in thefinal outcome