Hardhome was much different from the books, but was absolutely incredible. Having the Night's King and the WWs play a more prominent role was a nice way of highlighting what the REAL threat to the realm is.
The Dorne subplot wasn't that good in the books to begin with, but the alternative here was much worse. The whole thing was handled terribly, and so far it's felt like a pointless diversion--although it's been hinted in interviews that something big might happen tomorrow. Outside of Siddig's performance and Tyene's boobs there wasn't much to enjoy.
Jaime's development from AFFC was thrown out the window like Bran due to his Dornish detour. They haven't done anything interesting with his character this season--but I guess that's an improvement over the sept rape from last year. I was really hoping to see his growth as a leader, and how he finally pulled himself away from his unhealthy fixation on Cersei.
No Ironborn.
No Bran and Company.
Cersei's madness was tamped down way too much. They highlighted Maggy's prophecy, but didn't spend much time on her paranoia over Tyrion and made her estrangement from her family seem more sympathetic.
Arya's training in the House of Black and White feels like it's been gutted of most of the interesting stuff from the books. She's only had one false identity, we haven't seen nearly as much of Braavos, and several parts of her training have been cut out. Nor was she blinded.
Overall, this has been the most inconsistent season I've watched so far. It's been all over the place in terms of quality; there are several episodes I'll probably never watch again, while I've watched the most recent ones several times already. The books that were adapted were pretty weak overall, which gave them license to be more daring in their deviations, but on the whole I don't think D&D's approach improved things. :/