Endings aside, Mass Effect, and the entire ME series, gave you a chance to make your own choices, and made you feel like those choices made a difference in the way the game played out. The Witcher series was also notable for giving players choices that mattered.
Knowing that the choices you make at the beginning of the game may affect the way the game is played out, do you worry about making the wrong choice? Do you go back through a game with a different decision to find out how the game changed? Or do you just stick with the choice you make and go through with it?