The climax atop St. Bart’s Hospital is legendary. After Moriarty shoots himself to ensure Sherlock has no "out," Sherlock is forced to jump to his "death" to prevent his friends from being assassinated.
The episode, written by Stephen Thompson and Mark Gatiss, is a "perfect inversion of expectation". For five episodes, we watched Benedict Cumberbatch’s Sherlock Holmes stalk through London, insufferable and invariably right. But Jim Moriarty, played with a terrifying, mercurial energy by Andrew Scott, didn't want to outsmart Sherlock; he wanted to destroy his reputation.
The Fall That Defined a Generation: Reexamining Sherlock's "The Reichenbach Fall"