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.
Most people think this short anime was really boring, but gee, you gotta be patient with animes. Once you get past episode 5 it becomes a bit more entertaining, and to be honest I didn't think it was too bad. Anyways, I heard it was bad but you know, i had to check it out myself and ya'll should too :D