There are some differences between impressionism and post-impressionism.
Impressionism:
Tells about the "light" and "color". Artists draw paintings with the color theory. The painting is drawn by learning directly from nature. The painters paint the subject over and over again in order to catch the exact color.
Post-Impressionism:
It uses impressionist techniques; they want to take the style to a whole new level. Artists use more emotion, patience, and expression their art. They would like to find the deeper meaning.
I prefer impressionist style painting, because I most like the simple art that uses the simple colors and simple light. This is the famous and popular style of art. Although this kind of style is non-realist and somebody don't like it since they can't understand the painting, this is my reason why I like that. In real life, sometimes we will feel more pressures and more problems. So we need space to get away from reality of life and release.
Reference: http://www.youtube.com/watch?v=ucsjYz0FGj0