Yeah, there's a big sub-plot in the books involving Dorne and some other houses that has been written out of the series. Also some people have been killed off that are still alive in the books even before this season. So the show is definitely going to be different out of necessity at this point, but I think the major points are going to be there. Jon Snow for instance. Book readers have been waiting years to see him rise!
Arya's story and the Iron Islands plot line are still catching up to where they're at in the books, but they'll be caught up pretty quick, I imagine. What we're seeing with Jon, Tyrion, Cersei, Sansa, those are all plot lines that are new for everybody, and so far very exciting.