When I played through XIII, I liked it enough at least to keep playing. Hope, Vanille and Sahz were my favourite characters (even if I used Fang, Lightning and Hope endgame), and I liked some of the bosses and the music. The Final Boss was entertaining. Tacked on, sure, but entertaining. Nice music. Not as good as for example Necron, who was awesome, or as good as the Undying, who was great, but good. Unlike some other final bosses in FF. Like Kefka or Emperor.

However, now I'm at the point post-game where I can do all the sidequests, and I just can't do it. It's too boring, there's no appeal in it. I wanted to get all trophies, but gave up, it's not worth it. I've started continuing my third playthrough through IX, spend two days straight doing nothing but grind for abilities on the beach on the lost continent on disk 3, and help, I enjoyed it more than the sidequests in XIII. I dunno, does that make me sad?

I blame IX being the superior game.

All in all, XIII is good when you play through the story with your brain turned off, but after that, it gets forgetable quickly. There's zero replay value, too.