With the game being released within the United Kingdom tomorrow, I figured I will give you a review based on what I think about the game (good old US versions). The game is basically much like the original Dissidia with a few new people in it with a few people changing sides. Such examples are Cloud and Terra joining Chaos for a bit and Lightning, Tifa and a few others joining the side of Cosmos aside with the original lot who are with whomever they was (other than Jecht whom switched over to Cosmos side).
Now the story basically focuses on the new lot and why they are not in the original Dissidia and focuses on something called Manikins – an army of crystalline clones of the warriors. Story wise, it does follow on directly with the original Dissidia as it is the cycle based before it. If you do not know what I mean by that, play Dissidia again. Now I will not stay much more about the story and will just move onto the rest of it.