Descartes was a rationalist which means that there has to be axioms somewhere or drawing logical conclusions is impossible. We all know that their are no axioms in human behaviour. We can change the universal constants at a whim just by thinking about them differently. He believed in god for example, which any modern philosopher would just say is an absurd statement. We can't say anything more about god than we could anything we can make up at the spur of the moment.

The rationalist aproach works great for maths but it fails anywhere else. Descartes saw humans as supremly logical beings, which we today know is false. There's not a lot in the brain that's logical. It's just a bunch of neurons connected in a way that increases our survivability rate. Instincts if you will. We may fool ourselves into believing we're logical because we can outsmart all the other animals, but that isn't saying much. Dogs are smarter than rabbits. That doesn't make dogs supremly logical beings. It's not that we're incapable of logical reasoning, we're just not very good at it.

Richard Dawkins effectively kills of Descartes in his book, "the selfish gene", and Dawkins isn't even a philosopher.

When studying philosophy at university, (grad school to Americans) there's an unhealthy focus on old crap that we since long moved on from. I consider Nietzshe being the stepping stone taking human awarness onto the next level. Anything before it is nice to know, for learning terminology if nothing else or for learning our philosophic history, but it has very little relevance to modern thinking. God is dead and let's move on.

I've read a lot of philosophy and I strongly recomend the philosophers Focault, Deleuze and Lacan.