The story of Dragon Ball unfolds gradually over 11 years of publication. The tone and the style of the stories gradually changes to reflect the tastes of the readers and the editors of Shōnen Jump in Japan. The early volumes of the manga (chapters 1-134) are primarily humorous fantasy stories, but they contain some minor sci-fi elements, much like Dr. Slump. Notable fantasy elements include not only the monkey boy Goku and the Dragon Balls themselves, but also many talking animal characters, unlikely martial art techniques, and identifying characters as gods and demons. Despite the fantasy elements, the world does contain highly advanced technology including hoi-poi capsules, space-saving capsules which are pocket sized but can store almost any object (including cars, planes and even houses) and other "near future" objects. The overall mood of the earlier volumes is light with few deaths and an emphasis on adventure and humor.
A subtle but significant change in mood begins after Goku's best friend Krillin is killed (the first of many deaths in this arc). This begins the King Piccolo Saga (chapters 135-194) in which the manga enters a darker tone compared to its earlier volumes.
Dragon Ball fully transforms into an action based shōnen manga at the onset of the Saiyan arc (chapters 195-241). Starting with introduction of Goku's first child, things begin to take a much more serious and harder sci-fi approach. Many characters which previously had fantasy origins (including Goku and Piccolo) are recast as aliens from other planets. Advanced space travel, alien threats, and powerful cyborgs and androids take center stage instead of more fantastic villains.
Awesome Manga. If you have time you should read it!!!