The process of translating Agamben has forced me to pay closer attention to his style, broadly speaking, than I likely otherwise would have, particularly given the necessity of following up on his references and citations in order to bring his looser European bibliographical style up to American standards.
First, it’s clear that for all the obvious erudition of his work, he relies very heavily on secondary sources — but primarily in order to use their own evidence to come to his own conclusions. To use our fashionable contemporary terminology, he is mostly concerned to make “interventions” into particular fields of scholarship that he views as having been held back by a lack of explicit attention to strictly conceptual concerns (which usually leads them to more or less unconsciously accept some pre-given conceptual form). This is clearest in The Sacrament of Language where he repeatedly shows how an anachronistic theory of religion produces “blockages” of various kinds in scholarly investigations into the phenomenon of the oath.
Second, he is seemingly obsessed with tracing the history particular words and phrases, which he — in a very Heideggerian style — views as having a certain conceptual inertia or “life of their own.” This became abundantly clear as I was translating The Highest Poverty and had to track down recondite references to obscure passages in already obscure Church Fathers who had used close variants on the phrase forma vitae. There seems to be a desire to resist translation, as evidenced by the vast tracts of untranslated Latin in his recent works on Christianity (a fact obscured by English translation standards, which lead many translators, including me, to supply English translations where he has not supplied Italian translations). But the resistence seems to be primarily to prematurely translating the terminology into modern languages and therefore modern conceptuality — he doesn’t share Heidegger’s skepticism of Latin translations of Greek terms as far as I can tell.
Third, he almost never cites his real dialogue partners explicitly. He’ll name-check them, which is helpful, but you don’t get the same kind of intense dialogue with the Foucauldian text that you do with some recondite German scholar. It seems to me that all the Homo Sacer books are in very close dialogue with Foucault — indeed, you could probably match each of them up to specific volumes of the lecture courses, with Homo Sacer itself matching up with the published first volume of History of Sexuality — but he doesn’t ever bring it to the surface. We’re “just supposed to know.” (This is even more pronounced with Arendt, who gets name-dropped as a major source in Homo Sacer and then more or less falls off the face of the earth.)
Finally, I’m going to make a somewhat bold claim — despite appearances, Agamben is not really a “systematic” thinker. I honestly believe that his Homo Sacer project was more or less blown wide open by The Kingdom and the Glory and continues to be blown open by the two volumes I’m currently translating (on monasticism and liturgy). Agamben is fundamentally a “local” thinker, even if certain concepts, gestures, and motifs inevitably occur, and I think a lot of the weaknesses in the book Homo Sacer stem from the fact that it’s just not “local” enough (and by the same token, the most suggestive and interesting parts tend to be extremely narrow, like the bit on werewolves). He’s not at his best theorizing in grand Heideggerian style, even though he clearly finds that very seductive and wants very much to do it — he’s at his best when he has one basic phenomenon he’s working with, with a clear textual tradition and a scholarly tradition that he can bounce off of. The difference between Homo Sacer and State of Exception is illustrative here — I think the latter is just a much better book, because it’s about something (how to conceptualize the state of emergency) and can ground its claims.
I’ve been taking part in a Lacan reading group this summer, and I think there are real parallels to be drawn between him and Agamben — both embrace authorial personas that are self-assured to the point of being arrogant, both are willing to dismiss whole scholarly traditions as missing the crucial conceptual point, both are more than willing to “force” their sources for the sake of clarification (as when Lacan reads the concept of foreclosure into Freud), and both give the impression of working out a coherent system even when their approach is, at bottom, more or less improvisational and experimental.
Finally, in both cases, their very obscurity is a big part of their appeal — it seems clear to me that the whole homo sacer notion had such a big impact precisely because people weren’t sure exactly what he was getting at. Agamben provided a concept that was malleable enough, and that brought together enough disparate fields, for a lot of different people to use it and respond to it. The same probably goes for Lacan’s pervasive influence on the French postwar intellectual scene, where people took the concepts-in-progress that he was using to synthesize basically every conceivable intellectual tradition and ran with them.