Another thing I felt, without having read the books, was that in OotP Umbridge's role was truncated. I remember people being very opinionated about her, they felt strongly one way or the other about the character. Maybe this tarnished my expectations a bit, but I was expected her to be more prevalent in the movie.
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You beat yourself up with your past. Don't blame yourself, blame the world. Blame God. Blame me.