Everyone saying that you can't have a silent protagonist in a movie - Wall-E was *almost* silent, and everyone loved him!
Not that that really answers the question, because silent protagonists represent different things in different games. Link and Crono, for example, are generally implied to speak without the player seeing the words, whereas Gordon is explicitly referred to as silent by the people around him. I thought it would be most ideal if the fact that Gordon doesn't speak an actual plot point - maybe his voice box is damaged and he hates voice synthesizers, or he took a vow of silence when his work tore Black Mesa apart or something. On the other hand, I wouldn't be too upset if he spoke, and although it would be hard to pull off an unexplained muteness I suspect that would be do-able too in a sufficiently artsy-fartsy film.