Ernest Hemingway said Mark Twain's Adventures of Huckleberry Finn began American literature. He'd know. This book is indeed great and one on the short list for THE Great American Novel, along with John Steinbeck's The Grapes of Wrath, Philip Roth's Human Stain or American Pastoral and Larry McMurtry's Lonesome Dove; among others I'm yet to read.
I read this for a book club and enjoyed discussing it as a group. It was a challenge for me to read it though. i had to make a conscious effort to pick it up each time, which is unusual for me when reading a good book.
I have no doubt about Twain's genius or the importance of this piece in American literature, but for enjoyability, it is not at the top of my list.