As you said in your reply to Matt, "Descartes was a man of his time." In my humble opinion, that's all that needs to be said.

Descartes also said he didn't believe God would deceive him. Today, and for roughly the last century or two, that sounds awfully naive.

It also sounds awfully naive to criticize someone for being a man of his time. We are all people of our time.

In the future, if we have one, our time will look awfully naive too.

Anyone, like Descartes, who achieves a major breakthrough in culture deserves our respect.