I do agree w/ the 2 disk theory. Dragonball (z, gt) is such an expansive series, they could have gone into such depth!! The game is pretty good though and has decent replay value. I already have over 35 hours logged on. I love the dragonballs in this game, although they are difficult to find!
If you are looking for an expansive DBZ game, i have "Heard Rumors" that the next DBZ game will be an RPG!!
I'm hoping anyways..