Look, I know that many of you are very discontent by the very un-cathartic ending. I agree that it leaves no closure to many of the questions we want answered, like "will Katou marry that 24 year old girl with that possible dead baby of hers?" and "What about the giant spaceship? Did that explode on Earth?" The ending is way to lazy and we all know it.
But I want to defend Gantz, because in my perspective, there was a solid ending that occurred a couple of chapters before episode 383. And personally, Katou and Kurono's love life and the exploding spaceship are secondary to what Gantz was trying to accomplish. For me, I interpreted the manga as a very philosophical work. It's about trying to find meaning, logos, in a world that seems to be none. It's a very existential work, not nihilist at all, with many characters coming to realize that meaning in life does not exist beyond what you make of it. Many characters suffered from the spiritual emptiness they felt, and Kurono especially abandoned any presence of God for Tae-chan. God, man, meaning, survival are all independent elements trying to find connection with each other. But that again becomes hard to accomplish when the giants appear and blow up the freaking planet.
Yet in chapter 370, all the philosophical questions become answered when the Gantz team meets "god" after Kurono kept on reminding himself that there is none. Well, he was wrong to a certain degree, because he meets that freaky behemoth who answers all the question. And it is here, I argue, where the story finds is closure in its symbolic level. The questions of god, meaning, and such that have been a plague to the characters as well as the readers that finally find some sort of resolution. After this point, everything else that happens is not that important.
What made Gantz so great was the ability to challenge not only the boundaries of manga in general, but also to challenge your mind. For example, I remember the exasperation when understanding the mental schism of Tonkotsu when the meaning of his life, his girlfriend, is lost due to the giants. But when he seeks revenge, only regret and despair, not catharsis, is achieved. Just how powerful those moments were, I can't seem to forget. The fight scenes, the overt sexuality (which I also have my theories on), and the amazing drawings were thing on the literal level that captivated the readers. But we also should consider the symbolic, and how the two registers interact with each other dynamically. I don't think we should consider Gantz bad because the ending had no closures. I mean, come on! The manga was never about closures, but opening up the possibilities since the beginning!
