Mainly the way they spawn. To be honest, I don't really mind it but I think it would make the game better if driffers, instead of spawning randomly, they spawn some distans away. It would allow the player to respond to them in more ways then just sword and armor. You could build defencive structures, arrow slits, pits, murder holes (in more realistic and historical way). I think this would make combat way more interesting, without needing to change much about what already is in the game.
I would really like to see what others have to say about it. And maybe if they believe my idea is flawed is some way. I am open for discussion.