The Cartesian tradition: thinking subjects attempting comprehend things/objects in the world. Heidegger: Dasein (being there) the subject is not behind a glass wall but immersed in activities, which often do not need to be thought about, in an already pre-given world.
The question that any practically minded person is going to ask is: what does this mean in practice?
Outside the field of literature and philosophy, I would say this: Heideggerism results in shifting the emphasis from rational thinking to intuitional feeling and from an attempt at absolute knowledge to relativism, (your truth is as good as mine). Heidegger can be seen as replacing the individual with a zombie-like conception of the human being in the flow-of-life.
Heidegger reveals some important aspects of human existence, but one should avoid over reliance on his philosophy.