Can't remember if you mentioned it in this thread - did you play XIII? It isn't required, theres a thing you can read to catch up on the story, but I can't imagine playing XIII-2 without having played XIII first. The story is pretty much a direct continuation, with characters from XIII popping up every now and again, and some of the relationships being critical to the story in XIII-2. Plus, if you like XIII you'll love XIII-2 - if you didn't you probably won't like XIII-2 either, although there are some improvements.
It's a better sequel than X-2 was, put it that way...
Only played VII & VIII. Should i start with XIII first? Probably get that for next to nothing now.