I don't read the books so I have no real comments on casting news as I'm unfamiliar with the characters. However, so far, I feel every actor that has been cast has done an excellent job, and I expect more of that in the future.
That said, Season 2 was significantly weaker than Season 1. Just felt too muddled. I'll most likely keep watching, as I'm invested in a couple of characters and I really wanna see Joffrey die (like, more than any other character in tv history), but it's not at the top of my list the way it used to be.