I covered a drama over a month ago that now has an A lister attached.
At the time, I knew it was out to this actor for consideration. I also knew in my gut that that this actor would risk it, even though the role went against everything the actor had done before. In particular, it was a combo of the character's manipulative trait and co-dependency.
How did I know then that the script had legs?
First, I could talk about the big set pieces, and the storyline without looking back at my notes. In fact, it's a month later and I can STILL tell you about the script. The main character has a clear purpose that's easy to explain, with clean action lines.
Also, there was a deep range of emotions for the actor to play. ex. The writer included several scenes where everyone else was talking about the main character. When the main character appears in the doorway, the combination of the gossiping and the main character reacting/knowing they were gossiping that gave the scene tremendous subtext.
Second, it hung together. I tried to stomp on it, peer inside, crack it apart, but it hung together. It was a lean script and only had some minor issues that were fixable.
WHAT I'VE LEARNED: The core of that story was its vulnerability. It was so real that you feared you'd lose the moment if you didn't turn the pages fast enough. Great stuff.