Well, I hated the protagonists, both of them. I thought they where badly written. They had these qualities, I guess they where written like that to become more human, but instead it made me dislike them. I am not sure what it was now, as it is at least 7 years since I read the book. One thing was that stupid hair thing with the woman though. How she had this oh so fantastic hair, but it wasn't very academic of her to show it off, cause academics are ugly and smart.... Stupidity! I did like the man author though. But that stupid marriage thing he had, where they didn't have sex, and that was the reason for his adultery. Why couldn't it be plain love? That is more realistic, that giving him an excuse like that. Oh no, he can't get sex with his wife, let him find true sex, I mean true love with someone else then. Most men who are having affairs get love and sex from both wife and mistress. Would it have made him a lesser man if he didn't have the excuse? Sure, but not more unsympathetic than the rest of the bunch in the book anyway.
The rest of the characters I found to be travesties of real people, very two dimensional, and kind of not very sympathetic. I thought they where better in the movie though.

And I hated how the author felt the need to explain to me all the time what the interpretation was, like I was too stupid to figure it out for my self. I thought she was condescending. It wasn't a very good experience for me as a reader, I didn't care for the main characters, eventually I didn't care for the mystery, and I found my self jumping over parts of the book just to see the end of it fast enough.

All in all, this is a very good case of where the movie is better than the book. Same with Chocolat too, a horrible book, but I loved the movie, very much because of Alfred Molina, who is absolutely fantastic in it.