Please stop using revenge as a primary motivation for your protagonist as it has become somewhat overused. It is also something I cannot identify with as the death of my family/loved one/dog would not cause me to stock up on weapons and go on a killing spree. I would probably just become a gibbering wreck instead, cowering in my room and crying myself to sleep at night.
On seconds thoughts, that wouldn't make a very entertaining game.
Stick with revenge.