I've been doing some really in depth thinking about Gantz and I know I'm probably gonna catch flack for presenting my theory but here goes. What if...all the people who participate in the game are really in comas, or just Kurono, and are really fighting for their lives. Gantz itself is the symbol of like in between life and death. If they get 100 points they awaken from the coma. At the very end of the series Kurono wakes up from a coma in the hospital. What seems like an eternity for him in the game could be in reality a year, a month, a week who's to say. He randomly encounters everybody from his coma but they don't know him but are astonished that he knows so much about them. The author probably planned this from the beginning as some kinda artsy abstract scratch your head kind of ending like Eva or Texhnolyze just to mess with our heads. It's been done before so I wouldn't be surprised. Maybe maybe not just a theory anyways.
There\'s no such thing as nerds anymore