LogFAQs > #983308559

You can read synopses for characters you've encountered, but in general, you might want to either play the first two games or read cliff notes of their stories. There's a decision early on that can help decide certain things that did or did not happen in previous games, so you'd probably get more out of that if you know the weight those decisions really hold. (I believe you face those choices after the tutorial area of White Orchard, yes?)

Just my two cents, though. I had only played a little of TW2 before tackling TW3 and it didn't really hamper my enjoyment of the franchise too much...'cause TW3 kicked that much ass.