Started the second book yesterday. First one was really good, especially as things heated up. I like all of the extra information.
There are a few scenes which didn't fit in the series. These are some of them, which aren't really show spoilers for anyone who's seen all of th4e episodes, but I guess they might be book spoilers:
When the Wildlings find Bran in the woods, Robb doesn't kill as many of them alone, because his wolf comes out of the woods as well and brutally tears some of their intestines out and shit. Then it eats a good portion of one.
When the other new recruits were to be made brothers of the Night's Watch, Sam was going to be left behind to have his ass beaten over and over in the yard until he was severely wounded or killed, but Jon speaks to the old maester and convinces him to save Sam by taking Sam on as his assistant (the maester is either mostly or completely blind, and both of his assistants at the time are illiterate).
Another thing was that when the dead man comes to life and Jon's wolf alerts him and he fights it and saves the Lord Commander, there is another dead man coming to life in another part of the Castle Black (they found two dead men, the two who had been with Benjen Stark's group of three) and it manages to kill four people. That scene isn't really shown in the book either - it's basically described to Jon after the fact.
Bran's dreams are more in-depth, and the crows talk to him while he's in a coma.
We actually see the battle that happens the night after Tyrion and Bronn and Shae are playing drinking games. Tyrion actually makes it into the battle, on horseback, and he even manages to kill one or two people, although at least one of them he basically kills by luck, accidentally causing the victim's horse to fall on him.
George R.R. Martin actually wrote the episode where Ned Stark dies. He changes some things from the book. For instance, Ned doesn't see Arya on the statue and tell Yoren to get her. Yoren finds her himself when she jumps down from the statue and makes a sloppy attempt to run towards the front with her sword. Later we find out that the reason Yoren is there at all is because a boy came to him and gave him money, and told him not to leave King's Landing yet, because Ned was going to take the black and go with him. It's left up to the reader to guess that the boy was probably sent by Varys.
The red comet shows up around the night that Dany puts Drogo on the funeral pyre, whereas it doesn't show up until the beginning of season two of the show, though season two pretty much picks up directly after that funeral scene.
The book has some brutal details. When Drogo is injured, his entire left nipple is lost. The night when Ser Jorah fights with the Dothraki outside of the tent where the witch is allegedly saving Drogo's life, Jorah has half of an ear sliced off.
Stannis is missing the whole book, just like the show, but it's implied that he's missing because he discovered the truth about Cersei and the Kingslayer, so he's already amassing an army and building a war fleet. (He normally sits on the king's small council and is master of ships). In the show it's not suggested that Stannis knows the truth until Ned sends a raven. Also, before he's killed, the former Hand, Jon Aryn, was planning on sending his son to be tutored at Stannis's home. It's suggested that this is because Jon Aryn and Stannis both know the truth. Jon Aryn's son is the sickly kid who's still breastfeeding way past what's normal. Once Jon Aryn dies, his wife (Catelyn Stark's sister) freaks out and takes the son back to their home and won't let him leave.
In one scene, Joffrey tells Sansa how stupid she is, and that if their first child is as stupid as her, he'll cut off Sansa's head and get a new wife.