I think GANTZ is the system that the creator of this world (God) has created in order to maintain the purity of earth's species.
the term "God" refers to a group of alien which had created and monitored the evolution of human kind since the stone age as their experiment or something. And for what ever reason, they have left our world, so Gantz was constructed as an automatic system to monitor the evolution of human kind.
the thing(human like) which are sitting in the black ball are something like AI which can think rationally but more like machines rather than humans, this is the reason why they work and response so straight forward.
Moreover, i believe that there are many machines orbiting around the world working for the following purposes.
- choose who to enter the room
- monitoring gantzer (bomb in the head and limiting the battle area)
- transfering gantzer, weapons, and what ever
- shoot to the ground when someone press the trigger of the pancake gun
- creating weapons, suites, bikes, mecha
**** What are the aliens ****
i think they are not all aliens but some of them are ancient creatures as we can see that many of them take the final form of lizard like.
Anyone have more to add please feel free
sorry for my stupid english writing skill