Over at I Cite I've posted a a preliminary sketch of my reading of Zizek's critique of Levinas. The post draws from Zizek's essay, "Neighbors and Other Monsters: A Plea for Ethical Violence," that appears in the book The Neighbor.
As I read him, Zizek's critique of Levinas has 3+1 elements, that is, three criticisms and a counter. The criticisms focus on: the big Other of the Symbolic order, the implicit privileging that results from the asymmetry of the call of the Other; and the Musselman. The counter involves Zizek's view that others are an ethically indifferent multitude.
Put in most general terms, the disagreements might be thought in terms of the ethics of the other. Zizek rejects this view, as he must with his basic assumptions of the subject as lack and of the symbolic other has lacking, incomplete. Any fundamental emphasis on the call of the other would involve filling in/covering over/denying the lack in the subject and hence eliminate the very space necessary for freedom. Additionally, we might say that unlike Deleuze (and Agamben?) Zizek does not equate ethics and ontology and unlike Levinas Zizek does not think of the ethical as pre-ontological/transcendental. Rather, for Zizek, ethics emerges in and as the gap within immanence, as the split or that cuts through our relations or interactions with all sorts of differentiated others. This split might be thought of as a no to these relations, as a calling into question their givenness, as a withdrawal from their everydayness.