I am very disappointed that the TV series isn't more faithful to the book series.
The biggest problem so far is Robb's marriage. In the book series Robb is tricked into marrying Jeyne Westerling when he is recovering from a wound in her families home after she seduces him into taking her maiden head. Having acted dishonorably by deflowering a girl while a guest in her family's home he tries to rectify the situation by marrying her. In the process breaking his oath to marry the Frey girl. We learn that Tywin Lannister orchestrated the entire thing and that Jeyne used herbs to keep from becoming pregnant in order to make a good match after Robb is killed. She is safe with her family when Robb is killed at the Red Wedding.
In the TV series Robb breaks his oath to marry the Frey girl for love and Talisa Maegyr (his pregnant wife in the TV series) is killed at the Red Wedding. I find it hard to believe that Eddard Stark's son would abandon honor and duty for love. Especially when you contrast it to Jon Snow (Eddard Stark's bastard son) putting his duty to his Brothers on the Wall and the oath he took before his love for Ygritte.
TV Series: Seasons 1- 4
Books: A Game of Thrones (A Song of Ice and Fire, #1) A Clash of Kings
(A Song of Ice and Fire #2) and A Storm of Swords
(A Song of Ice and Fire #3)