I had not the opportunity to read "GialloParma", so I decided to rent the movie and have an idea about it. In two words: a nightmare.
In my humble opinion, this is an authentic cinematographic failure, starting with the colourless acting and ending with the pompous score.
Everything in this movie is forced and unintentionally ridiculous, therefore the result is incredibly weak.
The screenplay, though written by the director (and famous writer) himself, is feeble, pretentious and never, never interesting. I really can't imagine how Bevilacqua could adapt his own novel this way.
The story: oh well, a plot DOES exist, but it's so patched-up and tortuous that it seems impossible to define it. Anyway, we can say that the picture depicts the (sexual, social and political) "crimes and misdemeanors" among the upper middle-class in Parma.
Finally, just an advice: it's ALWAYS better to read a book before watching its adaptation...