No. Only someone who watches and knows what the show's about would say that. You clearly don't.
Case and point. Why do people watch slasher films? Why do people watch porn? Why does the movie Wanted have so many good reviews despite it's shakey story? Why is Hellsing such a loved manga despite only being a gorey blood bath of Alucard wtf owning crap? Sometimes mindless sex, action, and violence is what the people want. Not every manga has have a complex plot like Death Note, Code Geass, or Ghost in a Shell to be as good as the before mentioned. If it's not for you, don't watch it.
But yes, the point of Gantz is crazy violence, sex, and gore. If you watched the whole thing, you'd know that.
Yes the best anime/manga have complex stories, action, and drama. I'm only on episode 5 and so far the story is good but there's too much unnecessary violence and beastiality. Please tell me if there is anymore beastiality.