Personality should be the main focus of this game.

I agree with the OP 100%--it's because of the entirely predictable personalities and sameness that I don't play much anymore.

Traits need to be far more dominant. If I give a Sim traits like angry, hot-headed and evil, I expect them to be in a sour mood most of the time, as someone in real life would be. Instead, a Sim with those traits is every bit as outgoing and friendly as any other Sim, and that's wrong