Play it for the awesome battle system, but don't expect anything else.
First of all, there is not much of a story to speak of in this game. The main character rescues an elf? girl and decides to accompany her. They are supposed to defeat her brother, who strayed to the path of evil. Overall, the plot is very forgettable. Compared with Grandia II, it is shallow indeed. The characters themselves are boring, and some of the voice acting are pretty bad, which doesn't help.
Now, for the shining part of Grandia III, the battle system. For those of you who never played any other games from the series, allies and enemies have their own icons that go around in a circular meter, and once the icon reaches a certain area within the meter, the character can then take action and whatnot. It's possible to delay or cancel an enemy's action, depending on its position in the meter.
Also, after an action is taken, where a character ends up is generally the new position. Often it's not a good idea for player controlled characters to bunch up together (against attacks that cover a big area), so that has to be taken into consideration as well.
There is no random battles in the game, player will trigger a battle when touching an enemy on the field. Certain types of enemies are so quick that it's near impossible to dodge them.
The difficulty is manageable throughout most of the game, with a few challenges here and there, but no major hindrance. Near the end of the game, the difficulty suddenly picks up somewhat, to a point where battles are a pain.
Fun gameplay, but that's about it. Gets really repetitive about halfway through the game.