What I picture him looking like is the guy who played The punisher, not the new one thats all steroid up but the first movie, idk why but that is what I picture Master chief as. He should play the chief in the Halo movie thats comming out to a theater near you in the year 2552 (the way there going, i wouldnt doubt it )
Why would they show Master Chiefs face? It wouldn't help the story out at all, and its not really important to anything. He doesn't have an identity, he's a soldier. 110% killer. He's more of an image or legend than a real person. Putting a face on him would kill that.
I heard that the face seen in the beta was supposed to be one of the game developers faces I will look for a source to confirm it. I still don't think they should show his face. If you want to see him as a child watch this trailer the boy is master chief as a kid.