I like unformed characters. This may be because, no matter how old I get, I am still unformed myself.
Something that you should take particular notice of is the fact that the best scripts have very few explanatory passages. Adding explanation to the descriptive passages of a screenplay is the most dangerous trap you can fall into. It’s easy to explain the psychological state of a character at a particular moment, but it’s very difficult to describe it through the delicate nuances of action and dialogue. Yet it is not impossible.
I have no idea who the characters are, later, their personalities take over anything I might want to do. I end up writing not from my own will, but from theirs-they come alive as I write and make me do things that I couldn't have planned.