The problems with Brokeback Mountain are so obvious that it feels dumb to list them. The opening act moves at roughly the speed of the glaciers that built the mountain in the first place. The conclusion undercuts the movie's entire raison d'etre: Don't worry -- there's still heterosexuals to keep everything going! (In that sense, the movie is like Jack Twist's father, who insists that, while Jack might have spent the best moments of his life on Brokeback Mountain, he'll end up in "the family plot.")
Most of all, though, there's the fact that the protagonists spend the entire movie manifesting exactly one personality trait each.
It made me think: Do characters have to change? Must we be subjected to yet another "arc"? Why is a story about people who get in ruts and stay there somehow unsatisfactory? And I was glad, on reflection, that I didn't have to watch Heath Ledger shouting "Jack!" and running from a church to embrace Jake Gyllenhaal in view of the evil sheriff who will shoot one of them the next morning or anything like that. But saying that stories are sometimes cheesy or mechanical doesn't mean your movie is going to fly without one.