Based on the manga Gantz, Gantz: O follows a man who, upon dying, is teleported to a small room with a large, black orb in it. He learns that he must "play a game" with a few teammates in which they will be teleported into battles against vicious monsters. Should they die, again, they will be dead for good. However, if they "score enough points" they can earn more weapons, be freed, or resurrect dead teammates. The team is forced to survive and adapt as they are dropped into a warzone of terrifying beasts.
This CG-animated film from Japan, based off the manga of the same name, was nothing short of controlled chaos. The story is interesting, but doesn't seem to have any direct purpose. The scenario is regularly referred to as a game, and has many elements of a game, like a scoring system and objectives, but the battles appear based in reality. The monsters just spawn in the streets and wreak havoc while these super-suited dead people try to kill them. It seems like the game has been going on for quite some time, and based on the level of destruction, it would seem difficult for Japan to be anything more than rubble by this point.
And there is no reason for the game. Not that there needs to be. There is a brief reference to aliens being the cause, but that sounds more speculative than anything. But it does make sense...these aliens, allegedly, could have turned Earth into their own personal game show for their amusement. SHOW ME WHAT YOU GOT.
The overdramatization, which for some reason always seems worse in CG and with the dubbing on, does get old. Many of the characters spend their time gasping, running, and over-explaining their motives. Yet, there was plenty of time set aside for violent action. Tons of dismemberments and exploding heads to go around.
The monster designs are the highlight of the film. Their are dozens of different monsters, some with multiple forms in true Japanese tradition, so it was fun to visually explore the film's massive creative universe. It was entertaining at the very least, but not much more than that. Eye candy for the action-horror inclined.