When I was studying English at university, one of my subjects was Historical Linguistics. At some point, we were given the beginning of a novel written in an imagined English of the future, in order to study the supposed changes that the language had undergone in the intervening time. When I read those first two chapters of "Riddley Walker" by Russell Hoban, the utter desolation of the contents, combined with the linguistic and narrative ingenuity of the style, gripped me and has not let go until this day. "Riddley Walker" is one of the best novels I have ever read.
What's original about this novel is its refusal to be categorized. The concept, the world from the point of view of a 12-year-old boy called Riddley Walker, living in post-apocalyptic Kent, England, would make it a science fiction book. But it's much more than a "clever" book. Riddley's world is not sexy or enchanting, it's depressing and mystical, as shown most strongly in the form of the mythical martyr/villain Eusa, whose "Eusa Story" cryptically describes the nuclear holocaust (read the text aloud if you have trouble with it):

Eusa had thay Nos. uv thay Master Chaynjis. He run them thru the Power Ring he mayd the 1 Big 1. Eusa put the 1 Big 1 in barms then him & Mr Clevver droppit so much barms thay kilt as menne uv thear oan as thay kilt enemes. Thay wun the Warr but the lan wuz poyzen frum it the ayr & water as wel. Peapl din jus dy in the Warr thay kep dyin after it wuz over. Mr Clevver din cayr it wuz aul the saym tu him poyzen wuz meat & drink tu him he wuz that hard.

The cautionary tale that is the "Eusa Story" illustrates the morality that has emerged from "Bad Time", as the war is now known, a morality not unlike that of medieval times: technology and engineering are the cause of all of life's woes, and we would do best to steer clear of them. And so Riddley's world seems stuck in the mud forever. But the novel's plot revolves around the first attempts to break free of this heavy burden and return to a society that sees the benefits -and disasters- of human invention. The book refuses to say whether this is a good thing or not, but it leans strongly towards pessimism. Hoban does a remarkable job of bringing these kinds of high-level philosophical issues and social developments to life, especially considering the main character's age and his limited perspective of the world he inhabits.
What makes the book especially harrowing is the lack of sentimentality and the straightforward way in which Riddley describes cannibalism, radiation poisoning or killing a boar. His encounter with Lissener, a horribly mutated boy, and their subsequent discovery of a large computer mainframe in Canterbury, makes clear that such things are trivial compared to the destruction and loss caused by Bad Time. Or, as Riddley puts it: 'O what we ben! And what we come to!' I could never appreciate this novel as much if it was merely crafty or ingenious; it's here, where it grabs you by the throat, that its full impact is felt.
Remnants of our culture remain in some form in Riddley's universe, but everything has attained a new form, meaning and interpretation, whether it's puppet theater, a touristic leaflet, or the English language itself. The mutated English in which the entire book is written, does make it difficult and seemingly pretentious; but as you read, you discover that it could not have been written in any other way and still be believable.
It's this credibility that gives the novel its status as a masterpiece: believable characters in a believable and fully explored society speaking a believable language. This, as Anthony Burgess said about this book, is what literature is meant to be. "Riddley Walker" is fiction at its utmost, literature stretched as far as it will go. It is depressing, mystical, difficult, a puzzle, a work of literary art and a science fiction novel, all crammed into some 200 pages. It took five and a half years to write, and it shows. Read it; it's unlike any novel you've ever read before or will ever read afterwards. Then reread it, again and again, and find new things in it every time. I do.