I feel since they've treaded into book 4/5 territory the show has surpassed the source. It is cleaner and more concise. They obviously didn't want to have the enormous cast from the source so they've simply merged some characters and made other characters replace others. They've breezed over and completely ignored some of the "feinted" and worthless storylines (like the prince of Dorne trying to woo Dany ... still could happen I guess)It's a little frustrating that they are considerably off-book in all the main storylines right now. Dany storyline is off book, Tyrion, Jon Snow/Sam/Gilly, Sansa/LF/Boltons... all off-book.
They are blazing their own trail now, and it's good, but bad too. I kinda wish it was following the book storylines more closely, but at the same time, cutting out so much of the nonsense in the books is a good thing.
The next year waiting for season 6 to start is going to be frustrating.
I think so far the most telling thing they've done is killed off Barristan. We could still not exactly know what will happen in the books obviously but it appears whatever Barriston is doing in Mareen won't matter and Dany just comes flying back. Again just glancing over what Barristan is/was doing in Mareen in favor of a cleaner storyline with Dany as the primary ruler.