First, kudos to narrator Elijah Wood for bringing this story to life. Excellent job.
Yes, the N-word appears quite frequently in this book. If you can't bear to hear it used even its historical context, then don't listen to this book. Personally, I'm glad that Audible did not produce a bowdlerized edition because in general, I object to sanitizing books just to meet the current social norms.
In any event, Huck Finn is a masterpiece and Mark Twain does satire better than anyone I've read recently. If you take this book at face value, then you've missed the point; this is not the cute adventure story that you first encountered in a children's version of the book.
This one gets 5 stars across the board. Five stars for the story. Five stars for the narration.