I feel the FFXIII trilogy would have been MUCH better had it just been a standalone experience. I personally don't think FFXIII-2 and LR had any reason to be included. FFXIII-2 basically retcons Lightning and pals' actions in the first game. Time travel just didn't work in favor of the story. Yeul this, Yeul that, eh shattapu yo face! Caius and Yeul recreating the (in)famous Lifestream scene in FFVII felt cheesy, and just made me go "Y U COPY FFVII??" FFXIII-2 was still a good game in its own right though. Managed to platinum both FFXIII/2. I'm still waiting for PR to hit that $20 or less sweet spot.
As to what made me get into FF, it would have to be Advent Children. I've seen and player a few of the past games before, but the movie was what finally got me into the games.
Edit: I'd have to edit famous Lifestream scene into infamous. It was a really unexpected scene, and it wasn't really a scene that was favorable to our party.
XIII-2 doesn't retcon it at all. It's actually the complete opposite, the point of the game is to correct everything so what happened in XIII stays the truth.