A quote from this paper by Nikolas Kompridis entitled Heidegger's Challenge and the Future of Critical Theory that I came across on the sidebar of Habermas Reflections.

Heidegger's various analyses of the phenomenon of world disclosure -- of In-der-Welt-Sein, Lichtung, Gestell, and Ereignis -- represent his central contribution to 20th century philosophy. Through these analyses Heidegger developed an original critique of, and an original alternative to, the representationalist epistemology and the naturalistic ontologies of modern philosophy. He marshalled important new arguments (both transcendental and hermeneutic) against mentalistic accounts of intentionality, against views of agency as disembodied and disengaged, and against "deworlded" conceptions of objectivity and truth. In Being and Time and in The Basic Problems of Phenomenology, Heidegger argued that prior to confronting the world as though it were first and foremost a physical object, or as though it were identical with nature, prior to establishing explicit epistemic relations to the world "out there," we always already operate with a pre-reflective, holistically structured, and grammatically regulated understanding of the world. (And so our theoretical understanding of the world always refers back to, as much as it draws upon, a concerned practical involvement with what we encounter in the world.) The notion of world disclosure refers, in part, to this ontological preunderstanding --- or understanding of "being." Heidegger's investigation of conditions of intelligibility -- of how something can show up "as something" in the first place -- took up the radical mode of questioning initiated by Kant's transcendental deduction, but cut much deeper than the epistemologically-curtailed and monologically-framed question of conditions of possible experience. One of the hugely important conclusions of his investigation is that if there is to be any understanding of something "as something" at all, "[u]nderstanding must itself somehow see as disclosed, that upon which it projects."