... Well written.

- Branco

I struggle with writing short, declarative sentences, they always grow into crazy run-on affairs with too many additional clauses and such.

Just watched Resident Evil: Retribution and it has this wonderful exchange-

Grunt: What are you doing?
Alice: She's alive, I'm going to get her.
Grunt: I didn't lose this many friends so you could just walk away
Alice: I plan on coming back
Grunt: Don't do this. You're more important than she is
Alice: That's where you're wrong
Grunt: This is a mistake
Alice: Get out of my way

Cliché-ridden dire-logue that is performed by two actors who know it's bad writing and don't even bother putting any effort into it. It's quite excruciating to watch. I contribute nothing else to this thread.

Firstly, everything Mike said is accurate and well put, anything I add will be the gravy to his steak.

Films are moving pictures with sound.  Images have a grammer and syntax as much as the dialogue do, so for me I describe good writing by the fundamentals of the images we are seeing as well as the dialogue is spoken.  A director, cinematographer, and production designer are going to play a important role in ARTICULATING those images that are described on the page, but the fundamentals come from the page.  This is much in the same way as the director, actor, and editor ultimately shape how the dialogue is spoken, performed, and shaped, but the dialogue is more or less what was on the page.  This is partially why I champion comic books so much.  Comic Book writers are in many ways more like auteurs because they have much more direct control over how the words are brought to life. 

So for me there are scenes that are perfect storms of the dialogue and image that convey the specific thoughts thoughts and feelings, and everything is working in a balanced manner to deliver this.  Michael and Fredo's talk in Cuba from Godfather II.  Rocky and Adrianne's first date on the ice rink in Rocky.  John Goodman talking to George Cloony before he mugs him in O Brother Where Art Thou.  Everyone of those scenes has text and subtext is communicated with it's choice and flow of dialogue that parallels the text and subtext of what's happening visually is a good metric of what is good writing.