Half-Life, I could see as a movie, especially if it carries over the atmosphere, but Portal? It's largely a puzzle game that has some story. Can't really see it as a movie property.
Totally disagree about Portal. The story was the driving force of the game for me. And Portal 2 added a hell of a lot.
Not trying to knock the gameplay. It's a perfect blend, but there is a lot you could do with that property, film-wise.