Great cinematography
You've really nailed the style of cinematography and camera moves from those epic Western movies. Also, the art direction is generally fantastic. Simple shapes, suitable for animation, and yet the texture you added gives it a bit of complexity also. Great coloring, also. You also had convincing characterizations. The old man with the white moustache, and the intense stare, was particularly memorable. Oh, and the progression of action was good. It complemented the music nicely without being entirely dependent on it (example, the line "and that's a dead man" often coincided with someone being killed).
There was one basic thing that I'm not sure came out well, and that is the way that the whole ball gets rolling. Maybe I got this wrong, but to me it looked like the main character comes into a bar, sits down, and then for no reason pulls his gun on three people sitting nearby and kills them. Why should I be on his side, after that? A little later on, a scene shows all three on wanted posters, but then why does the sheriff and his men chase after him, if the men he killed were criminals in any case? So that was pretty confusing for me. If he killed them because he had some sort of specific grudge against them (was that it?), I think that should've been made clear in a scene before he came into the bar.