If Gantz makes a perfect copy of you when you die, why are Katou's and Kurono's bodies never found? Did thew author change his mind on how Gantz works?
Gant Z makes the copy just before it thinks you will die, then teleports the dead body to god-knows-where (what should bother you is how it managed to delete Kurono's and Katou's body parts from the cellphone pics in the first chapter, since everyone notices that the bodies dissapear shortly after the accident).
Gantz is, according to improvising from what the god/alien said in germany, effectively pulling from/manipulating the Akashic Record, the Universe's file storage system. this handily explains the cloning ability and where the bodies go (they're simply erased from history)
Starting off, then - what is the deal exactly with the cloaking devices that are inbuilt into the suits ? Izumi and Nishi continuously use them to great effect, there appears to be no specific time limit, they're in the basic non-upgraded suit , and Kurono and co. fail to use them on pretty much every hunt?
Same reason why it took everyone so long to use the swords, and why it took a veteran player to point out that they have a room full of war bikes. Gantz doesn't give you instructions. If you figure out how to use them, whoopdedoo. Otherwise, just keep fiddling with the buttons and hope you don't die.
"Hope you don't die" is a big issue. That one guy was cycling through the various suit modes and accidentally exposed himself to civilians, causing his death.
What really annoyed me was the thoroughfare shooting scene. First, he guns down 387 people. 387. What, did he activate the infinite ammo cheat before starting? More importantly, where the hell were the police?! You can't shoot 387 people in a public street with absolutely no interference from the police. It would have been a simple matter for a (Japanese equivalent of) SWAT van to pull into the road and unload a group of armored cops to kill him. Or even get a few snipers in position as he moves along. The special forces guys responded in a heartbeat to Nishi's school massacre, where were they when 20 times the number of people were being killed?
You can when someone in the government is pulling some strings to get a better Tokyo Team.
In the anime, why does the Gantz say that the Suzuki alien thing's catchphrase is "ha ha ha", when it should be "Yuzo-kun?"
Rule 1: Gantz lies.
The death rate in Japan is a bit over 9/1000 annually. The population of the Tokyo metropolitan area is over 13 million. Very conservatively, that means over 300 people per day die in Tokyo and environs. So okay, some of them are pretty old; let's say for the sake of argument that 90% of them are too old or otherwise unfit to be very effective if revived - not that that seems to bother Gantz much; he takes several people who are fairly old, a couple who are too young to be much more than a burden to the rest of the team, a dog and a panda (who, to be fair, did manage to earn 40 points offscreen somehow). That's still an average of 30 people a day for Gantz to choose from, and the best he can come up with out of that pool are the misfits we see?
Gantz does manage to get a couple of people who seem like they should be reasonably competent (most notably Tojo the sniper guy and JJ the karate master). It's just bad luck that their first mission (the Buddhist Temple) was the most deadly one in the series as far as the Tokyo team was concerned (Italy would have been worse if it had operated by the normal rules of "stay until all the aliens are dealt with," and Osaka probably would have been worse if they hadn't had the Osaka team as well).