From what I've seen, XIII-2 took everything XIII did right and shot it, chopped it into tiny bits, and disposed of it in a shallow grave.

XIII was an ensemble story with no real protagonist for most of it. It was about everyone in the party. That ws smart because, if you hated one or two characters, you could rest assured other characters would be prominently exposed and developed.

Lightning and Fang sucked so I had Sazh, Snow, Hope and Vanille to look to for something interesting; for characters I could empathize with.

XIII-2 is about two character's and one of the dumbest time travel stories in history. If you don't like Serah or Noel, it seems hard to actually like the game.