I'm reading the book and watching the series at the same time (not to compare, but because I didn't manage to read the book in time before the season started and I couldn't resist to watch it). The tv series is getting further away from the source material. Not for the better, by far. But it's still good in it's own merits. I just wish that they didn't spend 10% of the last episode's time with the unecessary torture of Theon's scene. But I guess they had to give something for the actor to act, or he wouldn't appear in this season.
Also, they're making Tyrion too "nice guy", when he's not. He's very flawed. I don't know why they are afraid to not have a clear nice guy for people to root for. Other series had flawed main characters: Sopranos, for example. Yet, people liked and rooted for them.