I think it would add an interesting dynamic to helmets in the game, such that the added cranial defense would come at a cost to visibility. Think about it - how many warriors walked around with helmets on a normal basis in real life? They usually only donned them during battle. So it would be normal to walk around without a helmet, but then just before a hard battle you make sure to put it on to complete your full armor set. Of course more open helmets, such as a skull cap, would have little to no effect on your sight, whereas a fully closed helmet might only leave a slit for you to see out of.
What do you guys think?
Yes you would see less, but why would you walk around wearing a helmet all the time like a goof anyway? Are you one of those "special" kids?