An adaptation of TF2 at least makes more sense with its cast of colorful characters.

I can't see Portal working as a big budget Hollywood movie. There's only two characters and only one of those characters speaks. I can imagine the premise working as a small scale indie project where Chell has to navigate Aperture Science like a Saw-esque death maze.

Remember when TF2 was suppoused to have it's own TV show on Adult Swim? Because that certainly went smooth, didn't it?