I agree. The biggest problem with this movie is the source material. I haven't read the book that the movie was based on. From watching this movie, I doubt I would like the book.
The movie itself does features a lot of great performances. The best being Michael Shannon. I do have one theory about the anti-climatic ending.
The reason Susan was stood up at the restaurant. Tony committed suicide.
Of course, that is just a theory. Also, did anyone notice couple of the naked women in the opening credits were seen later on, in the novel section of movie, drinking outside of a bar?