The cast has been mostly perfect, so far. A few of them, I was unsure of because they varied so much from the book description (i.e. Technical Boy, Easter) but I was not disappointed. I even like Technical Boy's depiction in the show better than in the book.
The music has also been great. I'm not a really big music person and I prefer the score to be mostly unnoticeable but the music in this show enhances each scene so well that I am actually planning on buying the soundtrack.