An exercise in style, mostly. I haven't watched the series, but given that the characters are just collections of archetypes, it's very easy to catch up and get into the swing of things. The animation is brilliant – particularly in its use of distorted perspective and skewed framing. And the music choices are inspired – a selection of jazz and funk tracks that bring the science fiction setting down to earth, and highlight the debts owed to hard-boiled noir. The characters are all flamboyantly-dressed Tarantino-esque smart-mouths (although the film does tend to disrobe the women to telegraph their vulnerability).
Piecing together what the film is about is an unhappy task. There is something to its notion that being free from the fear of death is the source of true liberty. It also seems to be the source of the main character's exhilarating martial arts and piloting abilities. An almost Buddhist renunciation of worldly attachments is married to the rugged individualism of the wild west.
The villain is the victim of a corporate conspiracy, who wants to share the pain he has been put through by releasing a chemical weapon in the middle of a city parade (uncomfortable parallels with the Sarin attacks in Tokyo are largely left unstated). As is typical in anime, the corporation does not get its comeuppance at the end (in contrast to the new Ghost in the Shell film, for example). Instead the only way out is suicide, of a sort. The filmmakers link this death drive to a sense of the numinous and transcendent, and end by asking the audience if they can tell what's real and what's make believe. The villain and hero are mirror images of each other, and the film may be warning the audience away from the alluring but nihilistic aesthetic they embody.