I've complained about this before with regards to the movie Aragorn. I don't see him doubting himself or his duty in the books. He DOES (in the books) become more kingly as the story moves along, and maybe Jackson is purposely making him a bit weak at the start in order to better show that transition, but I like Aragorn a lot better in the book.
I agree! Aragorn (in the book) never had any doubts about taking up his kingship. And he was a tested leader. Read Appendix A about the Stewards of Gondor. Aragorn saved Gondor from the Corsairs using the name "Thorongil".
I agree that it is lost as a explicit, plotted element. However, where I think I differ from the author is that I believe that Viggo and the other actors were actually able to project a lot of the spiritual elements through mannerism and expression, so that there is a deeply spiritual tone to the movie even though its not as explicit as in the books.
I agree with you that I prefer the Aragorn of the book - who is almost sinless, almost a Christ figure (the virtuous King who will be revealed). However, I completely understand PJ's need to give the character complexity and a development arc because of the different demands of filmmaking.