I didn't find it impenetrable so much as unconvincing. I kept going, "But...wait...what was the point? You made no point. Oh, okay, there's the point. But...there's no argument for it, just a forcefully stated perspective. Okay...wait, what was the point of that?" over and over until I decided that it was really more like literature than philosophy.

I found Derrida completely impenetrable. I forget how far I got into anything of his, but he seemed to start out by defining terms weirdly, and then get confused between his new definition and the conventional one when talking about it. I came away not understanding him, but also not sure he understood himself.