To recap a little of what I wrote in the earlier post, the book combines folk tale elements to make a larger adventure story. Taro is a lazy, greedy, thoughtless child raised by his poor and self sacrificing grandmother in a mountain district of Japan. He is also strong, brave and good natured, spending his time playing with his friends, the animals of the surrounding forests. (Here he is teaching them sumo wrestling.)
When a friend is kidnapped he sets out to rescue her, and success in this leads to a further search, to find his mother, who had been transformed into a dragon.
The most striking thing about the film is how closely it follows the book. Most film adaptations diverge significantly from their source material, with close correspondences mostly found only in the earlier scenes; but Taro the Dragon Boy stays close to the original from beginning to end. The story makes a slightly different impression in the different media. Both are episodic; but while the two larger plot arcs that the book divides into are still present in the film, the story seems to flow forward more easily and the division is not so strongly felt.
The visual style of the film is strongly influenced by the traditional ink wash painting that Japan learnt from China.
The background landscapes are all done in this style, and while the characters are drawn in a more typical animation style, their colours are also toned down to fit the scenery.
You probably anticipate that a story that starts with a lazy and thoughtless protagonist will have moral lessons about the value of hard work and consideration for others. In a sense, it does. Here is Taro after working for months for a manipulative landowner, taking the pay she reluctantly offers him, as much rice as he can carry (which he then distributes to poor villagers).
But the account of the hero's growth does not feel moralising. We are not invited so much to condemn the earlier version of the character as to share his realisation of the harshness of the world he lives in and desire to change it.