Although I agree that domestic violence is wrong and should be severely punished, I am not a fan of once and done with regard to anything really. Everyone makes mistakes in their lives. 6 games is a harsh punishment and sends a message right away. Plus you have to consider the possibility the victim made the story up. Look no further than Brian Banks.
Additionally, Ray Rice has really seemed to try and turn his life around. He has a lot to lose and seems committed on getting better. I have respect for a man that can look in the mirror and say "I need help".