Story: Brutal, gory, remorseless, violent. All part of the underage student killing glory. Student killing, you say? How could a government do such a thing? It's explained, and the series does a good amount of explaining about the program itself and the government that conducts it. Have to give it props for explaining the ones pulling the strings.
Dat violence, but I'll tell ya this; it's not all about the violence. On the outside at least. On the inside, they're beaten down, torn apart and ripped to shreds as their minds break to the twisted game they're forced to play. Players go insane, turn into psychos and some become a complete contrast to what they were before the game. It's pretty damn good and the author does it just as well here as he did in the original book.
Violence, psychological violence, spiritual violence? That's just dumb. But that reminds me of how the manga is different from the book: tacking on extra scenes that have no business in being there. It extends the mid-game scenes needlessly and even the climatic end-game. It adds a sense of ridiculousness and absurdity if not filler and padding.
Other changes are there, but if you didn't read the book for some odd morally related reason then it doesn't matter to you. For those who have some of them aren't too bad. The one at the well, for instance, I felt was for the better, lest the one there lacked development in the book. Aside from the padding instances mentioned in the paragraph above, the changes wouldn't detract from your enjoyment.
It's a long series, yes, but it's over a short amount of time. Sometimes it's almost if it's plodding and it could have been sped up a tad, maybe not for getting expense of character development. Here I mean scenes from the original. As time marches on, so do the weak as they get eliminated and only the strong, the cunning and cowardly (Contradictory maybe, but discretion is the better part of valor) remain, the story slows down. This might not sit well with the more bloodthirsty reader but sometimes it's needed so one wouldn't take the violence for granted, other times, there is such a thing as too much peace.
Art: You have to give it credit on the detail. Viseral in it's gory glory, it doesn't shy away from the mature stuff when it comes to violence and the aftermath when one is left standing. Unsettling, brutal, and stomach churning, it'll make or break your enjoyment of a good part of it. Sometimes it's almost over-the-top, other times it sends the message home. I can't entirely say I enjoyed the deplictions of gore, mutilation of bodies and grim details but it did highten the experience and fit with the overall theme of students and friends killing each other.
The characters, range from the good looking trio of heroes, other good guys and gals looking good and some ugly motherfuckers by the name of those who I call villains; Sakamochi, Niida and Froggy are the ones that come to mind, and it's noticeable. You can't avoid noticing how the doctors slapped their mama when they were born. And as it goes on, the line between beautiful and ugly as sin blurs as the corpses pile. No matter how good you look, a corpse is a corpse.
Characters: One of the main selling points and one of the best parts was how they develope the characters. A majority of them get some sort of backstory, a chapter or two displaying their past, some of their quirks and a bit about of themselves before they check out. They aren't nameless future coffin occupiers, but real humans with emotions and enough depth to make you care for a select few and become emotionally invested.
One of the mentionables is Souma, the hot chick. If she weren't developed, she'd just be hot chick, but with development, she becomes more than that. But with a few others alongside her, it's not always straight-forward. There's more to them underneath their exterior and truly, once again, the depth is what helps brings the manga to excellence.
Not everybody can be given depth as some become corpses before we can know them. That's life, right? I'm not going to hold it against it. To be fair, some of them become worm food before we can get to know them but some of them, worm food and other minors, are in the past scenes of other more prominent characters. They're classmates and all but I liked that. Sort of creates a connection between the classmates.
The villains, once again, or what can be considered a "villain", only a few are truly despicable. I'll just use Sakamochi as an example, the head of this installation of the game. To put it elegantly, he's a fucking sack of shit and wholely unlikeable. The author makes no effort in giving him the slightest sliver of characterization to make him likeable in any way. Otherwise, one might say it's due to the event they're thrown in and forced to participate in, but sometimes evil is evil, and they might be evil deep down. Simply put, villains are done well overall, natural evil Sakamochi or otherwise.
Overall: I loved the Manga series, but not as much as the novel. Excusing final comparisons, it's obviously a series not for everyone. The violence and overall mature subject matter will put some people off but if you can handle that, you'll get one of the greatest series on survival games with a cast that aren't just faces. Sometimes the characters even overshadow the underage violence that gave the book such notoriety.