I wasn't a really long time fan of the series, as the only two games I had spent a lot of time with were VII and VIII, which I loved. I had played a bit of XII, but it didn't really grab me, so for whatever reason, I picked up XIII and was just so impressed by its visuals. I liked the way the battle system worked and didn't really care that it was so linear. I'm not very big on side questing in games, so having no ambiguity about where to go or what to do was kind of refreshing. Only thing I really didn't care for was that I couldn't really over level, since it locks you to only certain upgrades based on where you are in the story. Because of that, I had to spend a ton of time grinding (I'm bad at the game) so that I could beat the final boss. That was annoying.
But overall that's a pretty minor complaint given how great the music was, how impressive the environments were, and how engaging the combat mechanics were.