Spoiler free version: Plot slightly predictable in places, main character development (you know, hero syndrome) and relationships are formulaic, but overall it's pretty good for character backstories and as a survival story. If you like violence and explosions, and I mean really like explosions, and perhaps like strategy and character development, you should read it. If you balk at the sight of blood, guts, or graphic rape, huge trigger warning -- this is not for you.
Btooom! has a formula that many of us have probably seen before. There is a game, game becomes real life, person who played game is main character and plays the 'real life' version of the game. This, combined with a Battle Royale-esque fighting/combat scenario (there is a good reason it's the top, gives us a slightly predictable notion of the character(s) who are going to come out on top - a.k.a., Main Character and Main Character's girlfriend... at least as far as the manga shows. Needless to say, you don't get exactly nervous when the manga taunts you with the idea that Ryouta Sakamato (aforementioned main character) may or may not have died.
Story: 32 people are transported onto an island, and are given explosives called BIMs and chips implanted into their hands. Their goal? Collect seven other chips and, with their eight chips, they can call a helicopter to escpae the island. The 'twist' is that, in order to remove said chips, the person has to be dead (or the hand the chip is implanted must be removed from the body, either works).
The main character, Ryouta, is a top-ranker and a debugger for the online game Btooom! that the real-life game is based off of, and it is because of this knowledge and previous stragizing that he is able to play the game as successfully and cleverly as he does. Immediately, he becomes friends with an older man named Taira and eventually befriends a girl named Himiko who oddly resembles his Btooom! girlfriend (five guesses as to whether or not she is, in fact, Himiko from the game).
The story follows Ryouta, his want to save as many people as possible from the island, his fear of killing, and the day-to-day survival of their little group. Along the way, they meet others on the islands, blah blah blah, some people try to murder them, blah blah blah, fourteen-year-old kid is creepy as shit, blah blah blah, explosions and boom boom motherfuckers.
Art: The character design is pretty standard, but the scenery is FREAKING GORGEOUS OKAY. All the leaf details and pretty pretty forests that kind of remind me of Vietnam War documentaries. Maybe that has to do with the explosions combined with the heavy foiliage, but I like the art well enough. It's not shockingly amazing, but it's either good or good enough, depending on what you look at.
Characters: If there is a major thing that kept me reading Btooom!, it would have been the characters. It's revealed that the people sent to the island are only sent there if they done fucked up in some form or fashion. People in what I'll call the real world, the non-Btoom!-ified world, send the gaming corporation names of the people that "don't deserve to live." Some of the best character development comes from showing characters that seem to demand either spite or sympathy, and showing these backstories to explain their characterization.
These backstories serve as motivation for each character that is important enough to get one, and flesh out the characters on the whole. Even the main character isn't spared from a backstory that villianizes him a little -- only of the first things you see is the verbal abuse of his mother, and that he punched his stepfather over them trying to seperate him from his online game. Some characters are victims and don't deserve their fate, and some characters deserve their fate a million times over. The backstories connect the characters to their personality and their motivations in-game, making for more complex characters with very real fears, anxieties, and worries.
On top of the, you know, bit where they're scared shittless that they're going to die. 'cause that's a big part of it, too.
Overall: Overall, I'm torn between a 7 and an 8. It depends on the endgame of the manga, where they go with the ending and the characters, how they handle the company that sent them all to the island, the epilogue to the manga. So far, it seems to be heading in an interesting direction. Since I'm rating it as it is now, I'm going to give it a 7.5, based on the character development and the great survival plotline. I'd suggest it to anyone that likes action, explosions, and character development.
There are a few parts of the manga that are really dramatic and most of the characters are extremely human, something that should be respected in an action manga like this. There are dramatic moments that show the bonds between the people in the island and give good looks into the psyche of each of the characters involved, and some of the storylines are outright horrific to imagine or poignant when the significance of the moment is explained.
Plus they don't skimp on the intestines. Bless them for the fact that they don't tease us with the stupid gore by just having it off-screen and showing character reacts (except in one or two places that are done so for dramatic placement, y'know). You make something about explosions, you best show body parts strewn about a forest. And they deliver, without making it a manga wherein you see organs every other page. They keep it at the right amount of gore and ecchi so that it's not every-fucking-where, but you appreciate it when it is.
Yay for appropriate amounts of blood n' boobs!
Note: Also includes implications of vagina.