Not enough music
It's important to note first up that Cowboys are nowhere to be found in this film. Bounty hunters are the theme of the day in this futuristic world, as the main characters travel the galaxy tracking down paydays and putting away the bad guys.
The animation visually is superb, a nice mix of cel animation & CG (computer generated) imagery, and the characters' personas are translated perfectly from the anime series, and some of the action sequences are among the best I've seen in anime yet. The only complaint I have about this is the music-while Yoko Kanno's soundtrack is very well done as always, there's just not enough...a couple of songs and a fight theme here & there, but that's about it. They could've put much more in!
Even if you're not a fan of the anime, this is one film definitely worth seeing-one of the best anime movies to hit the US to date.