Totally off topic, but if you liked Gantz in the past, but simply disillusioned from the suckiness it became, I got a recommendation.
Trans Formars running in Young Jump is much like Gantz… but simpler, coherent story.
Mission based, human side characters die constantly like nothing, grusome depiction, and the monsters look creepy, quirky, and funny at the same time.
The first volume told the first (although revealed in the story to be second) mission entirely, and wraps up the story in one volume.
The new mission arc starts from the second volume (coming out this month), and is being serialized in YJ.
I've read the first volume, and read a lot of blogs saying how it's one of the more enjoyable on-going manga now.
To summarize the scientifically silly plot
! It's 26th century, to terraform Mars human race put a special kind of mold all over the red planet.
Then they put cockroaches on the planet that eats the mold and multiply. They use these to warm the planet to melt the frozen CO2 underneath the surface.
! But the roaches comes across ruins of ancient alien beings, beings that triggered the evolution of sapiens on Earth… sorta like the Engineers in Alien/Prometheus franchise, or Proto Culture in Macross.
roaches evolved to humanoid form, but still retaining the insanely strong roach attributes.
They slaugther the human exploration team that came to check on the planet.
Humans use these "Terra Formars" gene to splice insect genes into human beings, creating Kamen Rider... er, I mean superhuman.
They are capable of fighting the roaches, and are sent on a mission with different agendas to the Mars.
It's fun as long as you don't take shit seriously. Got very similar vibes to early Gantz.