A very accurate analysis of the plotline (using that term loosely), the story is where i mainly don't see eye to eye with the game and is in need of the most constructive criticism.
I've noticed that in Dissidia when each character goes to find their crystal, it almost seems like you're repeating a dumbed down version of the original game, so in other words the storyline relys heavily on fanservice.
Putting the story aside, Dissidia can play out as a great fighter, there's a large amount of content considering it's a PSP game with some of the things like the Duel Colloseum, the Arcade mode, Online battles so in that sense it has good replay value, not to mention you don't have to force yourself to massively grind whilst playing. You can pick it up, perhaps do a couple of quick battles and spend 5, maybe 10 minutes playing and put it down again.
So to summarise, the story relys heavily on fanservice and is barely engaging to anyone looking for an actual plot, and even less engaging if you've played all the original games because you probably have a good idea of what sort of rehash they've concocted for each different "path". But the actual battle system is very flashy, it's fun if you want a short burst of gaming and it has a variety of content not found on alot of PSP games.
I just think Square Enix are just too lazy to write a decent storyline.