Brokeback Mountain has all the hallmarks of a classic western—cowboys, ropin' cattle, ridin' bulls, and campin' in the great outdoors. But it diverts from the classic western, generally a hetero-male power fantasy, by making its two protagonists redefine the term "man's man."
Any romance in a western is usually between a cowboy and a cowgirl, or a different kind of love: a love for the freedom of the wide-open West. Brokeback Mountain also inverts this. Its cowboys love each other, and they long for a freedom that the land cannot offer them.
Brokeback Mountain changes the way you look at any western. It makes you wonder what the cowboys are doing up on those mountains all by themselves. What goes on in those tents when the chapter ends or the screen fades to black?