I've been listening to the audio book of Agatha Christie's The Halloween Party, which is the book that A Haunting in Venice is supposed to be based on.
I have to say the book is a very typical Poirot story. It bares no resemblance to the movie. In fact the film is far better than the book. The whole ghost theme really adds to the story. So, yes, I do recommend the movie over the book. The book is an ok mystery, but the movie has a lot more to it.