I adore this book. I think it's important to flush your mind of preconceptions, though. For one, it's very much not a Batman book - he makes the briefest of cameos, and though Arkham is littered with familiar faces from his rogues gallery, it very much focused more on original characters and their voices than any existing ones. Secondly, it has little, if anything, to do with the Grant Morrison story, Arkham Asylum: A Serious House on Serious Earth, save for the location and title (though, if you've read my thoughts on the Morrison book, you'll understand that this is wholly a positive attribute, for my tastes). This is very much a standalone arc about a single character in a tiny corner of Batman's established mythos - and it's all the better for it, in my opinion.
The biggest chunk of the plot follows Warren White, the man who will come to be known as the Great White Shark. He is, as his nickname suggests, something of a shark - rigging finances, hunting loans, and basically being the kind of criminal that can ruin lives without lifting a finger. And when he is admitted to Arkham Asylum (by his own, somewhat selfish choice), the characters inside recognize him as even scummier than they are. It might seem a little hypocritical that the Joker, of all people, considers a loan shark to be a bigger evil than himself, but the hatred is palpable, and White needs to find allies on the inside if he hopes to survive against the menagerie of varied and powerful Batman villains.
That's the hook of the plot, anyway. The underlying elements, which form the somewhat psychedelic conclusion, are wildly different from pretty much any representation of Arkham Asylum seen before. And, if I'm totally honest, it's a huge part of the reason I love this tale. Ignoring that it's a unique, fresh spin on an established fictional institution, I'm always slightly dismayed (in varying degrees, depending on the story) by the representation of mental health in the Batman series. Arkham Asylum is painted as being either a dumping ground for actual psychotics, or an unfortunate mainstay of Gotham City's criminal element, or anything in between or outside of it. The worst of it, for my tastes, is in Morrison's aforementioned Arkham Asylum: A Serious House on Serious Earth, which vilified actual mental health (and perceived as mental health) issues to the point of being incredulous and disgusting.
Arkham Asylum: Living Hell seems to make the most strides, for my money, towards justifying the needlessness of a mental asylum in a modern-day environment. Not to spoil, because a lot of the surprise is in the reveal, but it's a very old-fashioned (and by that I mean old-fashioned literature) approach to insanity and horror, which, pleasingly, seems to absolve the blame for the human element. Arkham Asylum as an institution that breeds monsters rather than curing them is remarkably justified, in that the people inside are relatively blameless...! I don't think it's ever touched upon again, but that's a shame, because it's almost Lovecraftian in its romantic simplicity of externalized "insanity," and I like it a lot.
Dan Slott is on writing duties here, and a lot of his trademark wit is recognizable. Interactions between Warren White and Batman's rogues are almost always fascinating, if not outright funny. There's a dark undertone to everything (helped by Ryan Sook's pulpish, almost two-tone, slightly exaggerated, cartoonish artwork), but in many ways it raises the material from the murky depths. It's much more enjoyable to read than a book subtitled "Living Hell" might appear to me, and Warren White's transformation from a naive, thuggish criminal to a full-on Batman mainstay is bittersweet without being overtly tragic. Which isn't to say there aren't horrific elements to a story ostensibly about a haunted mental asylum, it's just it's so much softer and subdued than they could have been - making Arkham Asylum: Living Hell a more entertaining read than it could have been, had it been handled by a different creative team.
I as much admire this book for what it doesn't do as for what it does, but then, that's the treasure of having a character and universe and dense as Batman's; Gotham, Arkham, and their populace are deeply entrenched into most all of our minds. When stories like Living Hell come along, that challenge our preconceptions and re-arrange the deck, I tend to swoon - it's everything I appreciate about comic books and their place in popular culture, y'know? It helps, though, that Arkham Asylum: Living Hell is a prison thriller with horror elements that just works, thanks to a creative team that knows what they're doing. It's crammed with inventiveness, a ton of great cameos by recognizable faces, as well as original faces that have gone on to become beloved mainstays (Aaron Cash and Humpty Dumpty in particular), and is overall just a great story that is assisted fully by the fun it's having in the sandbox that is the Batman mythos. It sure ain't for everyone, but I love the hell out of it.