The more lighthearted, campy tone, the battle system, being able to swap jobs mid-battle, the openendedness, Paine, the music (I like J-Pop, eat me)... it's just a fun game that's not meant to be taken so seriously.
I hate all the holes in the story, though. (What do you do when there's a giant deathmachine waiting to activate and skullfuck the entire world? Throw a concert!) That and the fact that 99% of the monsters were just directly CPed from the previous game.