Story: Starts off with a middle school kid who watches his friends all get murdered by a mysterious "Red Man." He's sent to a special jail known as "Deadman Wonderland" (yes, we know the reason behind the strange name right off of the bat, imagine that) where prisoners are constantly putting on a show for the entertainment of the average cable viewer.
Also he finds out that the collars everyone is wearing slowly poisons you, and every three days or so you need to eat antidote candy. Or you'll die. Amazing what you can get away with in a privately-owned prison — apparently Japanese laws or the Geneva convention or whatever has no hold over them, presumably because they threw money at anyone looking to usurp their dystopia of doing weird shit to criminals.
The main character slowly finds out more about the prison and discovers that he is one of the handful of people who has a "Branch of Sin," and is required to participate in extra games, where the reward is enough money to buy the extremely precious candy, and the loser forfeits a body part.
Art: The art is pretty awesome. The character designs are great, the action scenes are really detailed. There's loads of blood and gore, and the manga shows every death or dismemberment in pretty gritty detail.
Characters: Pretty much every character in Deadman Wonderland is a criminal, obviously, considering the setting. Nearly all of the characters have a backstory, even the ones you only see for a few chapters. You learn pretty quickly that you shouldn't trust anyone in the prison... but after reading for a while, you see that the people who seem nice are just as bad.
The main character, Ganta Igarashi, develops about as much as everyone other main character in a shounen manga. The typical he gets stronger stuff and all. However, the closer he gets to finding out about what causes the Branch of Sin to develop in Deadman Wonderland prisoners, the more emotional turmoil he's subjected to.
The main female, Shiro (also, by the by, she is not naked or even close to being naked. She's in a bodysuit. I was staring for hours trying to figure out if she had a bullseye painted over her nipples or not), starts off as one of the ditziest girls you'd ever see. Fiercely loyal to a fault with strength that she doesn't always seem to comprehend, she's pretty typical. However, even she gets a dark and gritty story and transforms from Ganta's cheerleader and protector to a force to be reckoned with.
The side characters are really interesting as well. My favorite is, without a doubt, Crow, who shows up early-ish in Ganta's journey through Deadman Wonderland and sticks around for the rest of the manga.
Overall: I heavily enjoy reading this manga. The more you read, the deeper the dystopian future it's set in gets. The anime version looks prettier, and of course, is better for the action parts, but it's cut-off about a third of the way into the plot, and shows no promise of starting another season.
The manga doesn't promise a bright and shining happy ending for the group and isn't afraid to axe off characters even after giving them a backstory that makes you care for the characters, sometimes bothering to make you empathize with them as they're dying. The 'bad guy' changes constantly, and the manga doesn't lose momentum or repeat itself with the fighting situations despite the promises of weekly 'games.'