I've read Derrida (more than I wish I had), and there's no doubt he's a charlatan, and a symptom of the decline of certain parts of the humanities

This review of a recent biography tries to suggest there's something there, but it provides some amusing ammunition for the contrary view:

One of Derrida’s examiners at his prestigious high school, the Lycée Louis-le-Grand, wrote of his work: “The answers are brilliant in the very same way that they are obscure.” His work as an undergraduate was no easier to decipher. Louis Althusser said that he could not grade his dissertation because “it’s too difficult, too obscure.” Michel Foucault could do little better, remarking: “Well, it’s either an F or an A+.”

The Derrida portrayed by Salmon would have shared these doubts. His “nagging fear that those who saw him as a charlatan were right never left him.”

At least he himself knew!  You can't really get the flavor of how bad Derrida is without reading his wild misreadings of other figures in the history of philosophy.  As I said years ago, Derrida "devoted his professional life to obfuscation and increasing the amount of ignorance in the world: by 'teaching' legions of earnest individuals how to read badly and think carelessly....[H]is legacy is one of shame for the humanities."