So, I've always thought that season 5 got a bad rap 'cus the early episodes weren't GoT at it's best, the final ones definitely were but I've been re-watching it and it's honestly a lot better than I remember it. I just finished episode 4 and it's been great so far and even the first Dorne scene was awesome, it's just that it ends in a pretty shitty way, but the setup is good.
I think I might have had a different outlook on the early episodes because they weren't all these epic episodes with tons of twists and eventful moments, it was mostly quiet episodes that were very dialogue heavy and were set up for the rest of the season, which don't usually play as well when you're waiting a week between them.
I need to watch S5 again, but I still think it's by far the worst season. It didn't just begin slowly, it ended poorly for most of the storylines, too. Ramsay was at his dumbest this season with his 20 good men. Dorne sucked all the way through. Dany was spinning her tires and had a pretty blah season, too. Selmy's death was fucking dumb and the sons of the harpy just wasn't that well done at all. Arya's story fell a bit flat that season, too. Sansa completely backpedaled on her character, too, and just got more silly punishment. The storyline in the north wasn't too bad... until the end. The conspiracy against Jon Snow didn't feel that deserved or well written either.
Hardhome was a decent episode, though.
I think the issue is that with a show like Game of Thrones you need an ebb and flow of storylines at different points to keep things interesting. In Season 5 almost all the storylines are at sort of lower points, either receding after action or building up to some that would be later.