Somewhere I feel like it's a pity that this is once again a story with dead people being able to come back through 'magic/technology' and whatnot. Having death be permanent would have given it a lot more tension.
But I can't deny, seeing those past main characters return again is thrilling! With Tae and Kato back, Kurono will probably bring Kei back with his own points and fight towards bringing back his previous 'girlfriend' after that. Knowing Gantz though, things won't go smoothly and more people will die along the way, turning this into an endless cycle for Kurono. Especially when the people that helped summoning back his friend die, as he will feel guilty.
Now that I think about it, Kei was a double right? Her real version still exists, so perhaps Gantz will find it troublesome to return her. Well, time to find out.