For final fantasy fans, this game would be an absolute blast. Otherwise it passable.
And oh yer, crystallisation system is another brilliance, somewhat annoying that you can not undo previous upgrades. But I guess that purposed for added difficulty. The bosses in this game makes is well worth playing. If you are easily frustrated better not consider final fantasy. If you do however, you had better make sure you concentrate on upgrading your health and ability buff and rebuff abilities such as poison and haste, rather than strength and magic. it will really helpful when fighting the bosses, because, they have such gigantic health and deal heavy damage that your summons has absolutely no chance against them.
Like i said earlier, this game has a weak storyline. If you are able to get past that, then you are in for a treat. The map is relatively linear in most part and leaves little room for exploration. Also, what I would have liked is a little plat forming ability rather than just running and jumping from one end to the other which can get rather boring and annoying especially if you have oerba Vanille in your team.
I would rate this game 9*s out of 10 predominantly for the awesome battle system and occasional awesome cut-scene