I see Denethor as a complex, once-great, and tragically flawed character, whose weaknesses were preyed on by Sauron via the palantir. I've seen reviews that said that this complexity and depth are missing from the movie, and that he just comes off as shrill and insane.

Considering what a nice job the movies did with giving Boromir dimension, who I've never liked in the books, I was hoping for better--but they seem to have set it up so that the characters are in opposition (understandable, but I stubbornly maintain not necessary).