I like most of what's been shown so far. Although, having read all five books in the meantime, I do have minor issues with some "loose interpretations" by the TV show writers.
When it comes to new characters, I think they did a great job with the casting choice for Davos Seaworth, but Stannis could be better (I think the actor playing Stannis would have been much better in the role of Janos Slynt). Melisandre is OK, Balon Greyjoy is pretty much what I imagined and Salador San was surprisingly entertaining. Xaro Xoan Daxos might not be what I imagined, but I think the actor is doing a good job nonetheless.
Going back to the old characters - Arya is still awesome, as is Tyrion. I'm liking Varys more and more, so props to his actor as well.