The Jarhead look was so different that a lot of my friends who love him did not appreciate this look at all. It is a different persona. For me, it's the same Jake Gyllenhaal. 

I thought guys would like his buzzed-off hair, since so many guys do this. So, you don't identify him at all by his hair. I guess his hair is more a part of him, for me than for you. In some pics of him without hair, though, as I've commented on, I totally see the Jake I know. But mostly not. But you do. You are always looking at his eyes first, I think.
kathy