The early ones were simpler in style and storylines. Modern manga have more complex plots and better art.
Well, early Japanese manga were often focused on traditional themes and had basic drawing techniques. Nowadays, they cover a wide range of genres and the art is much more detailed and diverse. The technology used for printing and distribution has also changed a lot, making it more accessible to a larger audience.
The main distinctions lie in the artistic quality and the range of topics. Early manga had less sophisticated graphics and fewer diverse themes. Modern manga, on the other hand, boast high-quality illustrations and explore a vast array of subjects, appealing to a broader range of readers.