The music. End of story. It has the best soundtrack in the entire series. Let me see how many awesome tracks I can name off the top of my head...

The Castle, The Extreme, The Stage is Set, Ami, Only a Plank between One and Perdition, Shuffle or Boogie, The Landing, The Legendary Beast, Premonition, Under Her Control, Fisherman's Horizon, Waltz for the Moon, Mods de Chocobo (best Chocobo theme in the series!), Don't be afraid, Force your way, ... you get the point.

Triple Triad is also one of the best minigames in the series. I actually made a custom board for it and recreated every single card and played some games with my brother.