While the quest for the "great American novel" is misguided at best, if there was one it would be The Adventures of Huckleberry Finn. It's hard to imagine any fictional work better embodying the universal elements of American life and attitudes better than Twain's serio-comic masterpiece. Huck and Jim's adventures down the Mississippi River on a raft are not those of a boy and an escaped slave any more than Ulysses' Odyssey was about a king trying to get home—they are the adventures of the human race, particularly Americans, struggling for identity, moral purpose, and a sense of home that our national transience seems always holding at arm's length. Most of all they are the adventures of a population growing from youth to adulthood, from the carelessness of adolescence to the weighty business of establishing a national identity.
To be pruriently "offended" by Twain's language and liberal use of the "N-word" is entirely to miss the point of this novel. While he was aiming shots at racism and its proponents and exposing some of the evils of slavery, far more positively he was celebrating freedom over absolutism, knowledge over ignorance; the language he used was the language his subjects used, and where they were ignorant so was their vocabulary. Huckleberry Finn is too huge to be simply about one thing or reducible to an essential theme, just as America isn't about one thing. It is purposefully huge and unrestricted to embrace everything—good and bad—that was the nation Twain observed. Of course some criticisms are louder than others, but this simply reflects the climate in which he wrote.
It is the language, in fact, which most distinguishes the novel aesthetically and thematically. Twain's mastery of dialect, particularly Southern dialect, has remained unrivalled by American authors. That he is able to maintain Huck's uneducated voice and consistently bad grammar for the duration is testament to his genius, and also what draws us irresistably in. Of course the story is intriguing with its faked deaths, family feuds, bad Shakespeare, and endlessly changing identities (not to mention Jim's dangerous bid for freedom), but one gets the sense that even if the plot points were relatively boring we still wouldn't mind listening to Huck talk. His voice is so singularly his voice, far more than almost any other character in fiction.
But the significance of Twain's style is more far-reaching. He gives voice not just to an ignorant Southern boy, but to an entire nation (no small feat, considering Huck's unmistakable Southernness and the still-recent regional animosity of the Civil War). Huck is at once intelligent and ignorant, experienced and innocent, cunning and naive. His exploits are often boyish daring, adventure for adventure's sake, but just as often they are serious expressions of his developing morality and sense of responsibility. In this way they echo America's youthful bravado and rapid growth to maturity by virtue of necessity. Thrust on the world stage, America was forced to behave itself accordingly, even while displaying a distinct antipathy toward taking itself seriously. In many ways it didn't yet know how to be a nation, and yet in many others it had no choice but to assume the characterisitics that would mark it for the rest of its existence.
Ultimately it is Twain's absurd, brilliant sense of humor which forces us to pay attention. Multiple times in the course of the novel he winds us to dizzying heights of hilarity, only to drop us in the middle of some tragedy or deeply somber situation. Perhaps the best instance of this is when Huck finds himself in the middle of a family feud of comically epic proportions that suddenly reveals its darkest underside when he finds his new friend dead after an attack from the rival clan. But there are other, altogether lighthearted moments, such as the King and the Duke's "recitations" of Hamlet to a confounded audience of backwoods yokels (who nonetheless seem to understand it isn't Shakespeare they're witnessing).
Huckleberry Finn is one of the few novels that come close to perfection. Twain's mastery of language, his eloquence despite his chosen restrictions of dialect, his humor and his incisive intellect together form a complete literary achievement that makes most serious novels seem like picture books. It is at once wildly funny and inescapably sad, rational and emotional, universal and specific, vice-ridden and virtuous. It is, in short, the most honest tribute to the American nation that has ever been written, or likely will be.