Descartes believed in god and his arguments for them are quite flawed. His other arguments such as the cogeto though do still stand up, the problem modern philosophers often have his how he applys these principles and makes logical jumps, for example the cogeto only serves to prove there is thinking, not that a self or thing exists in order to think, something Hume attacks with is observation as to the lack of any existing impression of an abstract idea of self being obtainable through introspection. Alot of Descartes other jumps such as his criterion of truth though can be forgiven as he believing in god is able to use the idea of gods benevolence (and hence the idea god would not deceave him) in order to justify these claims. Also Descartes himself kinda leaves out his main arguments about gods for good reason, that being primarily that the church would have burnt him as a hertic if he tryed... life in the early enlightenment wernt all that great for philosophers despite the name.
Anyway that aside, the idea of the indubitably of though remains true.

