3 choices you make in the story.
Don't shoot your mother
Don't forgive your father
This will give you the U.F.O. ending which means on your next playthrough (new game) you will get the laser gun from Joshuas bedroom in the house, so you just play the 1st part of your new game without the laser gun. Up until you reach the house.
But it's worth getting as it really does make the game easier (unlimited ammo with powerful laser shots)