I read Vance's book and the movie rings true to the parts of the book it chooses to represent. It misses the political and social commentary of the book, but I disagree with criticisms that Memaw or Bev were overacted over caricatures. Assuming Vance knew what he was talking about more than the critics -- after all, it was his life and his family -- then I think the portrayals by Close and Adams are faithful to what Vance wrote.
The book is better than the movie, in my opinion, but I thought the movie brought to life the characters in the domestic melodrama that was the generations of the Blanton family that Vance both loved and needed to escape.