The film builds up to this scene right from the beginning and it does not disappoint. Though Shane wins, his act is also an act of sacrifice since it essentially forces him into exile. A great scene both in terms of acting and editing.
Technically, Ethan's nemesis is Scar, but the climactic scene in this film is really a showdown between Ethan and himself. A virulent racist who can't stand the thought that his kidnapped niece has become one of "them," his first instinct is to kill her. When he says, "Let's go home, Debbie" instead, that represents the true outcome of the battle between good and evil.
I've long thought that Tombstone is a terribly underrated film (not to mention Val Kilmer's performance as Doc Holliday - how is it that the only recognition he got came courtesy of the MTV movie awards?). Tombstone actually has two great showdowns: the legendary battle at the OK Corral and the climactic showdown between Wyatt and Ringo.
Sergio Leone truly lets the viewer savour this scene, allowing Henry Fonda and Charles Bronson to circle around each other for a while before finally firing their shots. It's not only a fitting end for a villain of the first order, it also fills in the missing pieces in Harmonica's history.
The ultimate showdown of one man versus many. It's the kind of episode that makes for instant mythology and the sequence in which Will Kane proves his mettle is easily the best in the entire film.