First and foremost, the "n word" appears nine times through the text, four of them clustered together in two adjacent paragraphs of dialog. Frankly, it sucks, and really does sully the experience of the book as well as my opinion of the Author. There are a few black slave characters in the book, but none are given depth or consideration. As I also said in my review of Peter Pan, the slur was as much a disservice to black Americans then (only a decade from emancipation) as it is today.
The villain of the novel is Injun Joe, referred to as half-breed without explanation as best as I recall. Not quite as painful as Peter Pan, but still several "Indian" stereotype checkboxes are used for this character.
A modern reader literally has to "get over" both of these things to be able to see the story. Yet, this story has both of these things, and I suddenly understand why I've never heard the story before. It is an archive of prejudices that went out of style for mainstream America before I was born, featuring the title character lying, skipping school, stealing, running away, smoking tobacco and somehow, ending up without lasting consequence.
Past the prejudices, the writing is good, and mostly everything feels like it could have happened. The first half of the book drags on, and there isn't much adventure, mostly endless mischief. Tom Sawyer does grow some in the book, but not as much as I'd expect. This book kept my interest, but mostly because of the historic context. This is, in part, how children acted in the 1830s, and what a small Missouri town about a mile off the Mississippi river was like. Many of the places written about are real, and I'm fond of history.
Ultimately, I cannot recommend the book. There were parts of it that I enjoyed, but the parts that made me uncomfortable pretty much outweigh the overall experience. If you've read the book, and think I have it wrong, let me know... I'm happy to hear from others.