Modern games always want to put in "moral choices" where you can choose to be good or evil. Some dress this up with something like "paragon" vs "renegade" or whatever.
The problem is that these aren't really choices. They're a choice. You would get the same flexibility with just choosing a good or evil character at the beginning. Occasionally you'll get a player that strays, but for the most part it's both rare and not very interesting to do so.
The answer isn't to choose a different set of personality traits. The answer is to ask questions whose answers will change.
The fundamental personality of a character doesn't generally change. Instead, find a facet of the character that will change with the situation.
How about emotion?
What if your choices aren't about being good or evil, but about whether the situation has made you angry or happy or confused or stressed out...
Talking about your emotions in a video game is probably not about changing the outcome of the event. It's probably more about changing how your party members feel about you. The progression of the fundamental plot arcs can be based on the character's built-in personality (IE, it doesn't change much with player action), while the way your party members act, their powers, and their AI can be based on your character's emotional activities (which are probably largely the same as the player's emotional activities).
Let's give a Jedi-based example. You and your buddy are Jedi. As such, you save a politician from being killed by an angry mob, then respect his diplomatic immunity and have him deported. This is in line with your personality: Jedi wouldn't let a lynch mob get away with murder, no matter how deserved it is.
How do you feel about it, though? Are you angry at the politician for being so horrible and getting away with it? Angry at the the mob for not acting properly to address the concerns legally? Disappointed in the failure of the system to protect citizens? Can't get your mind off the hottie leading the mob's charge? Feeling totally zen about the whole thing?
Your chat with your buddy will allow you to tell him how you feel. In turn, this will change how he considers you. You're angry? Your buddy will focus on playing the calm and collected guardian, and get better in powers like pacify and defend. You're disappointed in the system? Your buddy will learn skills to help manipulate the system - the "red tape Jedi". You're completely zen? He'll allow his own anger to come through...
This seems like it would be a whole lot more interesting than simply choosing "good or evil". Especially since a player's emotions can change! You don't have to be angry all the time! That wouldn't even make sense! If a player selects "angry" even in response to children playing with puppies, you can put him in anger counseling or something.