I'm quite fond of Stannis' casting, too. I thought he worked well in season two but in general the casting has been excellent. The only character that hasn't been working for me is Jon Snow, a character I liked a lot more in the books.
I'm don't like the Jon Snow actor at ALL! He is the only weak actor in the cast for me.
But they cast Tryion, Twyin, Jaime, Ayra, and Ned perfectly. I'm fine with one miscast character.