What is the difference in the attitude and feel of Old Who and New Who?

I get the impression that New Who is far more serious, that the Doctors show a lot more emotional maturity and pain than the old Doctors, and that their relationships with their companions are explored in a deeper level. But, of course, I've only seen one or two Old Who episodes/films. Which is why I'm coming here - to those of you that have seen both, how would you describe the feel of Old vs. New Who?

Edit: I think the fact that New Who takes place after the Time War and the Doctor is the last of his kind changes the mood of the show dramatically. Yes? No?