I have read all the books, up through the 5th book and so far I am upset with this season as well. Not because of bad acting but more because it seems they have left out some very big characters/plotlines that I saw as being hue for the coming books. It makes me upset because while I was reading I thought they were going to be huge going forward in the Song of Fire and Ice series, but the fact they left them out in the show makes me wonder if they are significant at all in the coming books. I wont say which ones, but I am sure the people who have read them know what I am talking about. C- grade so far for this seaso.
It has been well documented that the TV series starting with this season is taking a very large divergence from the books. About the only two story lines that are for the most part untouched as of right now are the Wall and Cersei's story - and all that can change very quickly. Sansa's and Littlefinger's stories are beyond canon now and going in a completely different direction than what Martin has released in his preview chapters. Tyrion is taking a very different route to get to Meereen, and ultimately they're going to have to rewrite what happens in King's Landing to some extent because Varys is accompanying Tyrion there. We're not even going to get introduced to to Arianne Martel because they're only going to do the Sand Snakes (and when you get right down to it she's basically a useless character in the books other than to explain certain things about Dorne as they introduce it to us in the upcoming weeks).
If you are looking for book purity in the TV show, you might as well stop watching now. They've already said the TV show is going in a different direction.