Yup, totally agree with pride being the critical difference there; and you put it beautifully. I have a hard time being too judgmental of Denethor because in Tolkien's world he was created as a counterpoint to Aragorn - it's sort of a chicken and egg issue, but as a created character he lacked the free will to alter his fate. He was who Tolkien created him to be. And he did have a lot of good qualities, I think.

If you're interested, telperion1 put together a nice synthesis of references to Denethor

Edit: oh, I almost forgot I did a little analysis of Aragorn and Denethor a while back too, if you're interested
http://meckinock.livejournal.com/87491.html#cutid1