Simply, human

There's an article up at Cinematical on movies with well-rounded female characters written by men - their examples include Alyssa from Chasing Amy and Lianna from John Sayle's Lianna. I'd also suggest almost anything by Joss Wheaton, as well. Monika Bartyzel, the author of the article, suggests this:

The best rationale I can offer is that men who can successfully write women are those who don't try to write as women. What I mean is -- they write naturally and rationally rather than with specific and often stereotypical tropes in mind. There might be classically "feminine" elements to the story, but the path and thought behind them is, simply, human.

And, of course, I'm not saying that we should let things lie status quo. Some men can write truly beautiful female characters, but the world still needs more screen words written by a women's pen.

Spot on. I think this is inextricably linked to the idea that women are an Other, that we are indeed Bugs Bunny in drag - women are men dressed up in eyelashes and lipstick.

This notion has come up a lot in the Sotomayor nomination, that because she is a woman, a Latina, she can't be a blank slate (ie white, male). Women aren't human, we're something different all together. And to some screenwriters, this idea is just dominates any dialogue, which results in massive, dominating, suffocating stereotypes.

I was watching The Garage last night and turned it off after 30 minutes because the female romantic lead was just ridiculous. Matt, the main character, had some level of nuance, but Bonnie Jean was basically a cardboard cutout that moved. The main scenes I saw her in included her walking up to Matt's car (all legs and breasts, thanks cinematography) where he asked her out after just learning her name, and then their date which included classy shots of her clothes choices, them driving around and then making out. The character had no substance; she wasn't human. She was a teenage boy's fantasy in flesh - a beautiful girl just wanders up to a boy, says yes to a date, and then makes out with him. Very few (if any) girls exist like that in real life.

Once screenwriters, directors, cinematographers, and movie industry folk start thinking of women as human, we'll actually see more realistic female characters - you know, as fellow humans.