This review may be a bit short so please excuse that, I reviewed the first 'season' or 'part' but really it should be watched and reviewed as a whole.
My review for the first part had a decent amount of cons, eg. the characters being unreliable. Swapping from being scared in the beginning, which is completely understandable, then being strong, but then they would bounce back to being scared and strong and it just repeated. That left me being kind of unimpressed with the first 'season'. But, having watched this, it doesn't get rid of how they were in the first half, but this half is much better.
Kei is fighting for his life and so are his new friends and acquaintances.
Some of the things in this are a lot more intense, especially the Buddha Temple mission. That on it's own was better than the first half entirely. That's what makes me regret not reviewing it as a whole and doing it as the seasonal parts it's split into. It really needs to be considered a whole, as that's what it is. Between the two there is no break.
If you decide to watch Gantz, make sure to take that into account.
This half doesn't hold back on the blood and gore, surprisingly there's probably more than before. The characters develop to a place where they're enjoyable and the good points of the first half carry over, like the intensity of everything, how rough and raw it is, the blood and guts.
The plot for the entire series is entertaining, different and a great idea.
It's dark and when it gets into it, can have you sitting there in anticipation wondering what could happen next.
It is a good series, it has it's flaws that stop it from being as great as it could be. The very end is a bit confusing and just flat. It doesn't end answering any questions, it just gives you more. Though I don't regret watching it because I still enjoyed it as a whole even with the flaws.
If you enjoy dark, bloody and strange, then I'm sure you'll enjoy Gantz.