To sum it up, your decisions will do one of two things. It will either:
A: Alter future dialog (or minor details), either directly or after calculating multiple decisions against one another. Or...
B: Delay an inevitable plot-point until you're back on the same track either way. Every single character that can be optionally saved/killed/abandoned will die/leave somewhere in the near future regardless.
It's nice how many old decisions get referenced often, but it's really no more groundbreaking than Mass Effect, to give one example.