I loved the film, and still do. It's one of the things that got me into anime, many years ago. I bought the entire manga in one go, eventually, for about 140 quid, and I still consider that money well spent.
Everything is much better developed when the time constraints of a movie aren't in place. Various important characters from the books, for example, were reduced to background characters without lines. Akira himself isn't just organs in jars, and Kei's psychic potential is far better explored. I wish I had it with me so I could read it again, actually.
tl;dr, film is good, manga is better.