I've ranted and raved about this in the forums a bit and decided to review it. Anybody that has seen the movie and felt that it had a lot of great ideas but needed to expand upon them, you need to pick this up.
Let's start with the protagonist, Kaneda. In the movie he's very much the rough around the edges, adventurous hero with a good heart. That's fine for a two hour movie, but in the first volume of six, each with 400 pages, Otomo has more room to play with the characterization. Kaneda is very much the desensitized urban gang leader. And Otomo has a more space to deal with the biker gang culture. In the movie Kaneda is thrust almost directly into the military's affairs, while in volume 1 he is merely skirting along the edges of it while trying to avoid it, but can't thanks to Tetsuo's involvement with Akira and the revolutionist girl he's interested in. It's apparent by the end of the volume that the military is going to play a much bigger role in volume two, and I can't wait to see how Kaneda tries to get even with both Tetsuo and the military.