Kant does represents a distinctively modern view of the human condition in contrast to that of ancient high culture, found in ancient Greek ethics and also in ancient Chinese ethics.

It is actually a nice question how far Descartes himself endorses the monological and metaphysically dualistic theory of mind associated with his name and his legacy in early modern philosophy. But Fichte does reject this tradition, by suggesting that an immaterial thinking substance is an incoherent notion, and a rational being whose rationality was not developed through communication with others is a transcendental impossibility.

It is rational to choose the right means to your ends to develop very elegant abstract formal theories of rational choice, and then turn these into what look like moral theories. Philosophers tend to be ravished by the formal beauty of such theories, and they don't pay much attention to the fact that our human limitations make them pretty useless in practice, while the simple point about instrumental reasoning is too shallow to be of much real moral interest.

In fact, if you read what Kant has to say about feeling, desire and emotion, you see that he is not at all hostile to these. He is suspicious of them insofar as they represent the corruption of social life (here he follows Rousseau), but he also thinks a variety of feelings (including respect and love of humanity) arise directly from reason - there is, in other words, no daylight between the heart and the head regarding such feelings.

People are often most proud of precisely those things of which they should most be ashamed.

Kant has been famous for his rejection of eudaimonism, but I think Kantian ethics has a great deal in common with Aristotle, and some things in common with Stoicism as well. The traditions tend, I believe, to talk past each other when it comes to happiness or eudaimonia.

Freedom is an unprovable but unavoidable presupposition, not an article of faith.