To sum it up in one word, I felt betrayed. The original books shed humorous light on so many of the rotten things in our world, in a way that had protected me. For example, I had met the Vogons before I encountered actual bureaucracy. This book depicted Vogons as people complete with awkward father/son reconciliation plot. I was certain when I read it that Adams was 'spinning in his grave' as he would have put it. I was inconsolable.
I had to opportunity to read the final manuscript in preparation for interviewing him. After reading the manuscript, which was difficult as I became increasingly upset as I slogged through it, I refused to be involved further and suggested that they not publish it. When further begged for interview questions, the best I could come up with was something along the lines of "How dare you?".
I've often felt that the series lost its free spirit and lightness and became incredibly personal towards the end. Maybe it always was incredibly personal. I don't know if it's true or if it's just Douglas's depression. The time with Fenchurch feels almost like a stolen glimpse of a very private moment.
Some points also to Eoin Colfer who didn't make a total hash of the sequel book, which I imagine is a very difficult thing to approach and would inevitably upset a lot of people.