A friend of mine is screenwriting these days. I can't say much about his work except to say that I think it's very good and pays very conscious homage to its inspirations, among them the classic movie Chinatown. Reading Jon's work, inspired me to go read Robert Towne's script for the movie. I've dabbled in screenwriting, but I don't think you have to to appreciate the brilliance of the work. There's a reason people call it "the greatest screenplay of all time," and a good summary of it (and the screenplay itself) is here. Spoilers may follow, reader, so proceed at your own risk.
I'll have to re-watch the movie, too. Some people will think this is crazy, but I think I like the screenplay more than the movie, which i acknowledge is among the Greatest American Films. What strikes me about the screenplay, reading it all the way through for the first time, is how it does so much with so little; part of the art, as I understand it, is to not just move the story along with brief scenes and only a few lines of dialogue, but to see if you can pack the dialogue with the weight of the enormity of what's happening in the life of the character. Too, Towne uses every ingredient to its fullest. For example, the opening scene with the cuckolded husband, Curly, not only establishes the kind of dirty work protagonist detective Jake Gittes does for a living, it establishes Jake's character, his cynicism, and sets up his relationship with Curly, which will be used much later in the film to make a much needed getaway - well, two getaways, one that succeeds and one that fatally doesn't.
The other thing that strikes me about the screenplay is how dazzlingly complex it is. Count the crimes being committed that Jake uncovers, layer by layer - adultery, murder, theft on an enormous scale, graft, fraud and, well, you know if you've seen the movie. This rot and corruption, and the paranoia it creates, was so much a part of the American 70s zeitgeist, created in part by this movie, which mirrored what was happening in the lives of the nation, and it's rarely been so perfectly expressed.
Last point: I love that the movie creates personal symbolism with its title and references to Jake's earlier work in Chinatown. Because it is personal symbolism, the movie might have been called "Beverly Hills" or "Venice Beach." Maybe those locations don't suggest, as Chinatown does, the experiences in Jake's background that cause Chinatown to become a symbol of corruption, of a place or situation where an investigator, a crime stopper, cannot do his work, a place where things get turned upside down and where someone trying to help instead harms, but I love anew how vaguely this is demonstrated. Chinatown is Jake's - what - his Vietnam, his Marathon, his private hell, and now we, and all of America, are in there with him.