In Gantz, upon dying, some people are transported a special room, where they are assigned missions to hunt aliens and earn points to be revived. It's introduced as a fairly straightforward death game type manga, but as I understand it, Gantz was one of the first to use this concept, so credits where it's due. While this mission structure is fairly formulaic, there's enough creativity in the alien designs and action, to keep it feeling fresh. Because of this structure, characters are constantly introduced and killed off, the problem is that very few characters are well-written, so at best, the deaths serve as shock value, while in other places it can even feel comical. The main character, Kei gets some decent character development, and there's maybe 3 or 4 other male characters who have some nice writing, but all the others are quite one-dimensional, including all the girls and women.
The first female lead, the 15 year old Kishimoto was transported to the room by attempting to commit suicide, but it turns out she actually lived, and the one transported is essentially a clone of her original body, so now there's 2 of her walking around. Do we get to explore the mental state of a suicidal teenager who returns as a fake copy of herself? No, but we do see her naked body a lot, and she does get sexually harassed and assaulted, including by Kei. Then there's an adult woman, who over the course of a single night, has sex with and falls in love with our 15 year old hero. After them, we get Reika, who exists for the fan service of a sexy, popular girl to falling in love with and chasing the main character, and so the author gets to draw the same girl with big boobs naked for the chapter covers. Tae, who ends up with the protagonist in the end, is really the only girl approaching a personality, but you can't really say more about her other than that she's shy, socially awkward, likes to draw and is in love with Kei. There's also Tonkotsu, who gets some brief, but interesting stuff, so if you mesh all the girls together, you might get a single personality out of them, but most of their characterisation just boils down to which male character they completely fall in love with over a couple of hours.
The fan service doesn't just boil down to the treatment and depiction of the women though, but also the main character. While he does get some decent development like I mentioned before, but a large part of his characterisation is just "guy who is a loser in real life is actually a super cool guy, saving the world and getting the girls" type wish fulfilment. Because of all the fan service, it often feels like you're reading the author's self insert wish-fulfilment and thinly veiled fetish, instead of the plot he's creating.
And speaking of the plot, there's a lot of points that are either dropped completely or are completely shallow in how they are explored. The whole cloning/copy element is left unexplored, even when Kei himself is the one who gets a copy made of him, since it's just there to be fan service, where he gets to be with his modest high school girlfriend, and the sexy, famous idol at the same time. Vampires are introduced as adversaries, who are in cahoots with the aliens, but their whole plot gets dropped completely. Kei is presented as cheating on Tae by going on a date with Reika, but her memories of that get erased and they never have to resolve the conflict. At the end, characters get to ask godlike entities about the nature of the world and humanity, and the things they say are treated as this huge emotional moment, with characters having outbursts and breaking down, but the things they're actually saying are fairly surface-level, that most teenagers have as shower thoughts.
The thing Gantz is best at, is how it looks, although it's not without its issues either. Character designs are quite good, there is some same-face syndrome, but that's not a huge deal most of the time. The alien/monster designs are amazing, and the author has a great sense of drawing of drawing unsettling, creepy and outright scary expressions on them - to the point I'd definitely read a completely horror-focused manga from him, if he ever made one, despite thinking Gantz was bad. The backgrounds are apparently made in 3D first, characters get placed into it, and then the drawing are made based on that. This creates a unique feeling of the environment, that I haven't seen from any other manga. It's mostly good, but there are times when it's hard to make out what's happening, with the black clothes the characters are wearing on the darker, more shaded backgrounds. The action can also be hard to follow, the motions and impacts are a bit clunky.
Despite its many flaws, Gantz can keep you reading all the way through. Maybe it's the possibility that just one of the interesting questions it presents will be answered, or maybe it's just for the sheer absurdity of it all, which did make me laugh out loud, especially in the first half. It's not a story with a great plot, characters or themes, but if you can turn off your brain and indulge in the fan service, you'll probably come out liking it. People who think gore, violence, nudity, sex and surface-level questions about the nature of humanity are deep and profound on their own, without the necessity of good writing to expand upon any of them, will likely also enjoy it a lot. So I think it will continue as a relatively popular work, through it all.
