Isint Star Wars: The Old Republic a roleplaying game like Fallout 3?
I have no experience with it.
Basically, a huge part of the game is what dialoge options you choose, with everything you say influencing the path you take through the game. Hypothetically, you could play the same game three times and still feel different, depending on whether your a nice guy, kill everyone you meet, etc. Not to mention every class having a unique storyline.
EDIT: Perhaps I should clairfy. In KotOR II, if you were nice to the old lady you met at the beginning, you would earn light side points. If you were mean, you earned dark side points. These effected what powerd you could use how easily and what class you would later be. You could also influence your party, unlocking new storyline options, or other direct benefits.
In The old republic, I'm not sure if light side/dark side still exist. I don't think you can have a "good" bounty hunter, (your class determines your alignment) but influence on your comrades is expanded, with different options really influencing how your game goes.