Since I'm too busy to post my own stellar review, here's Jim Emerson's, via Roger Ebert's site.
I totally agree with Emerson's critique of 'provincial' big-city 'sophisticates' who are accusing the film of being 'closeted.' It is so clear if you watch this film that Ang Lee was not out to make a political statement. But by not focusing on the political statement, he made such a political powerful film about gayness and homophobia and our society's violent repression of gay love that even the right wing doesn't know what to do with it. The Catholic Church even initially gave 'Brokeback' only its 2nd-highest 'offensive' rating, only to be forced to switch to the highest offensive rating after zealouts complained.
This film is political art of the highest degree by virtue of the fact that it wasn't trying to be political. This is the tension I struggle with in my own writing and living. How to balance the need for real change in our world, policy change, political change, with the need for real stories, honesty, beauty, art?