GoT spoilers from the aired episodes and assumptions about the coming episodes:
Well the biggest deviation from the book is Sansa being married off to the bastard of Bolton. Essentially fullfilling Jeyne Poole's part in the books. But Sansa is the oldest living Stark, and for all Littlefinger and Roose Bolton are concerned, the only living Stark. She is a major player, and I don't see her sticking with the Boltons for long. What I think they will do is hurry Stannis' storyline along, he most probably won't go looking for tribesmen to help him fight. Which means with him having already killed Mance Rayder and talked to Jon, theres not a lot for him to do on the Wall. He'll likely march on Winterfell this season, which will be very interesting. There are a lot of moving pieces up North that need to be dealt with when that happens, and it will certainly be fun to see how they'll sort all this out.
Edit: That being said I thought about it just now and I don't remember anything from Sansas storyline from the books after Littlefinger kissed her in the snow. Not a thing. So maybe you should not take my word on this stuff. It's been a couple of years since I read the books.
The other thing is Jaime going to Dorne. Now I'm guessing he won't be caught prisoner or even be seen by the Dornish, as that would be a major incident and possibly spark a war. The one that almost certainly will die though is Bronn. I don't know why else he would tag along to this. Shame, a fun character, great on the show.
