The ending. Spoiler alert.
I love the movie. In the IMDB comments, several people made reference to the guys returning in the end for a higher moral purpose. I don't see it that way. Those four gunslingers had eaten crow once already when their guns were taken from them by Pierce and his men. When Pierce ordered them to immediately vacate land he claimed (but didn't appear to actually own), Russ Caldwell implores Frank Culpepper to stay and fight rather than give in to their demands. Caldwell essentially says he can't stomach being ordered by Pierce to get out--a second time, no less.
As they began to ride out with the company, their pride takes over and they borrow guns and return. I don't think they cared one iota about the homesteaders they would be protecting. If they had any good-hearted motive, it was to help the kid who stayed behind to face Pierce's men alone. And they couldn't live with themselves riding away from the fight knowing the kid stayed behind but they didn't. But I think their motive was to save face and fight the man who had humiliated them twice, not to defend the homesteaders on a moral basis.
The only thing I don't like about the film is how Russ and Dixie get shot. These are experienced gunslingers. But Dixie leaves his cover to preen in the open after killing a man. Exposed to the fire, he gets shot. Russ stops in the middle of the battle to admire the pistol he just retrieved from a fallen man, and is shot as he stands in an unprotected place. The fact that these two get shot because they become oblivious to their surroundings in the middle of a battle seems out of character for experienced gunmen. It reminded me of the old "Combat" series when Sgt Saunders' squad would be involved in a firefight with the Germans. Both sides would have good cover and the battle would continue until each German ultimately gave up his cover to stand in the open and get shot. It was as if the director didn't know any other way to end the scene. I got the same feeling when Dixie and Russ got shot in Culpepper Cattle Co. Otherwise, I think it's an outstanding movie.