I have heard about Gantz before, but after watching Corridor crew reacting to good/bad CGI where Gantz:O was as one of the subjects of talk regarding CGI, and the scenes they showed, it intrigued me.
Pros: Great CGI. When it comes to action it's awesome. So it's like 70-75% of the movie is enjoyable because of that.
Cons:
While watching I right away figured that this whole CGI animated movie character acting is literally dragged from anime style, and not in a good way. Anime is something where emotions are being conveyed through exaggerated expressions and dramatic situations that do not work in real life, but works in anime/cartoons because in reality it works differently, and by making anime grounded regarding emotions will look weird, and will not work. It looks cringy in reality as well when it's done vice versa, and since this is a CGI movie, it's like real life at that point, it doesn't convey well.
In this movie things do drag along, they are thinking way too long, making everything quite dramatic than it already is, and it's annoying. I am not even sure what's taking them so long to think about whatever they are thinking, but one thing for sure is that those moments are the silly exaggerated dramatizations from anime, and they do not work. It's like watching a drama soap opera or something. It should be more action packed, quicker thinking, etc.