Gantz tells the story of Kei Kurono and his friend Masaru Kato who die in a train accident and become part of a semi-posthumous "game" in which they and several other recently deceased people are forced to hunt down and kill aliens armed with a handful of futuristic items of equipment and weaponry.
Honestly, I forced to watch Gantz by my brother. The animation isn't that great, the story is hard to explain, and when you watch it at the end, you'll see how much of a waste oftime the show was. I've said this before for other shows, but this is another show that guys would probably like a little more. I do dig action, but I hated this show.