Since you mentioned me, I'm gonna solidify my opinion that XIII is one of the best Final Fantasy games. While I do think it takes a little long to fully open the game up, by the time it does open up they will provide you with all you need to be an ace at the battle system, provided you didn't just auto-battle your way through it. And the battle system is what makes this game to me. It's just a whole ton of menu-based fun. Cancelling orders at the perfect moment to sync up attack times to keep an enemy launched, reworking your strategy on the fly, it's just so exciting and hasn't gotten old.
I'm actually just starting up XIII-3 right now and I am so damn excited.