Gantz: manga review

Now, I'm really into one comic titled "Gantz"
The story begins with the death of the hero "Kei Kurono", 17 year-old high school student. He sees the society as boring or tired or something worthless, and one day he was in the station waiting for the train, the man who is drank fell on the rail, and nobody try to help and just call someone, but one tall guy decides to help, he is "Katou Masaru", he happens to be Kei's old friend. And Kato cannot lift the drank man up alone, and helplessly call for help to other people, but nobody want to help because the train is about to coming. and Kato finds Kurono, and asked him to help. Kurono jump on the rail and helped the man, but they were ran over by the train. They die.
One of this manga's characteristic point is that its picture, drawn by using computer, and its graphic is so real, and sometimes very glotesch and erotic.
And the graphic is becoming better and better as volume increase, not volume 29 is already published and if I look back the graphic on volume1, I realized the progress of graphic.

After death of heroes, they come to the room where Gantz is in, and there are other people either already, and they start to think that place is heaven or something. but see through the window, there the ordinal view is spreading, but they can not go out from the room. And there suddenly the Gantz which is black cube suddenly displays that their lives are under Gantz's will, and they are forced to kill aliens.
Gantz then give them special black suits and gun that look like toy, and then send them to the world that is completely same as the world they live, but they are invisible to other people, and there are aliens. anyone try to go home and go beyond the border the bomb implanted in their brain explodes, they are completely under Gantz's control.
and they find alien and start fighting. and this loops goes on.

the best thing in the manga is that the fighting scene is overwhelming, wigh fantastic graphic and scenario. the scenario is somewhat a little philosophical, featuring the human being's sin.