With that in mind, please read on.
First some details. The anime is 26 episodes long, and is more like a soap opera than episodic. Each battle, from the beginning, to when they have killed the last alien they are sent after, spans multiple episodes. It focuses on a few people, and one in particular. It also has a lot of blood, gore, and death. There is also nudity and sex so if you are not in to that, or should not be watching it beware.
Now what i think. The anime may be 26 episodes long, but it should have stopped at 21. The last battle (set of episodes) really serve no purpose and only raise questions that it does not answer. For example why does Gantz target Kei Kurono for death as an alien when up until then Gantz was using him as a hunter.
If you look on the web for an explanation you get a few. I will look at a couple of them here.
One is that it was is suppose to be an unwinable game. There are several problems with this view. First you do not give out super suits, trackers, and lethal weapons to those you are intentionally sending out to die because it raises their chance to live. Besides the jerk that I was happy to see die had survived longer than Kurono and was not targeted.
Another was that Gantz was pissed at Kurono for trying to shoot him in the head. Unfortunately, this does not wash. First off a powerful bomb is placed in their heads when they first arrive. Why not just trigger the bomb, end the season/series and start with all new people if there is a second season. Or teleport in a bunch of people and target him right then instead of waiting weeks.
There are of course other “explanations” in the forums as well, but I am sure that you can see why they don’t work. So I will wrap this up since this post is getting on the long side.
If they had ended it before the targeting of Kurono, I would probably have given this an 8. But as it stands with all 26 episodes, it deserves a 3. For no ending is better than the ending that they gave us.