Let me start out saying that I like Descartes and his Meditations. I remember my first philosophy class ever in high school when we learned the meaning of the phrase "I think therefore I am". It was an 'aha' moment for me. What do we really know for certain?
Descartes' Meditations explore the idea in a great deal more depth. Paragraph after paragraph he breaks down some of our assumptions. And it's kind of gratifying, right? We don't really know anything. It feeds my nihilistic tendencies, which just feels simultaneously good and bad.
Which brings me to my point. What is the benefit of his Meditations? Sure, he works on reconstructing faith in the world around us, but I don't think that reconstruction is nearly as powerful as the deconstruction at the beginning. I'm left thinking that he's right to doubt everything, and furthermore, he argues that if our mind was a result of random chance and not a perfect diety, then our mind is likely flawed. Actually, that's a possibility too, isn't it? Maybe "I think therefore I am" makes perfect logical sense to us but actually holds no true meaning in an absolute sense.
So I love the exercise, but it brings me to my bigger critique: what then is the benefit of wallowing in doubt? If I believe I exist and the things I sense actually exist, maybe that's good enough. In fact, living life and taking existence for granted seems to work out better than having your head in the clouds all the time.
Maybe it should actually be "I think, and that's good enough."