Great fun
The tiny details really make this movie into one of the best I've seen on Newgrounds. I say this because you have the cowboy panting as he reloads, the gun smoking after you shoot, the empty shells falling from the gun and bullet sounds from enemy shots hitting your cover. This is good stuff.
On other aesthetics, the pictures look good enough. The enemy cowboys don't look as strong as your main character.
I also really liked your choice of music. The music from Trigun are are all outstanding because it suits this game competely. The fast tempos are already made to suit a gun-slinging atmosphere, and this game's theme is no different.
You really did a great job on this and look forwards to your next project(s)