There are many characteristics that make Manga very distinctive. The largest thing that Manga art is known for is its characters. Manga characters almost always have large eyes, small mouths, and they also usually have abnormal hair color. These things give their characters a very western look to them. Manga like Akira, however, has gone against this grain.
Manga characters usually show over exaggerated emotions. When a character cries, it usually pours out in buckets, when they laugh, their face seems engulfed by the size of their mouths and their eyes become slits. An angry character will have rosy cheeks and steam rolling from around their body. This use of emotion would most likely be categorized as cartoonish.