Agree with all this.
I have found this season weak so far, with more disappointing or pointless sequences than great GoT moments. I think they have literally as well as metaphorically lost the plot.
This interesting article proposes why: https://www.theguardian.com/tv-and-radio/2016/jun/13/game-of-thrones-season-six-is-wasting-all-our-time
Aside from the interesting whittling vs. sculpting metaphor, I found that article largely the same as reading the complaints on the ASOIAF reddit. That is not to say I disagree, it used to be that The Walking Dead that would make puzzling and frustrating decisions, which I would then contrast with Game of Thrones, a show that was almost completely devoid of them. These last two seasons have closed the gap there somewhat, although HBO is still a far, far better network than AMC (as well as the gap in achievement level between their respective source material, which really shouldn't even be an insult to TWD) and it shows. I have found myself wishing for Fargo season 3 (probably my favorite show currently on TV and an excellent watch if you haven't yet seen it) in the midst of the season climax of Game of Thrones, which would have been unthinkable a year or two ago.
I disagree that Riverrun was pointless. Sometimes, scenes are about the
characters, rather than affecting the political plot. In fact, I'd argue that the Riverrun plotline was far more valuable than Jaime's entire jaunt off to Dorne; it has singlehandedly revived Jaime's character arc and development/redemption, while Dorne "gifted" us with the worst line of dialogue I have seen on TV in a
long time, and I watch The Walking Dead.
Also surprised to see as much angst about the Blackfish among the fanbase as there is. He was rather a minor character, and the difference in his escaping (in book) vs choosing his death (in show) can be traced to a couple important bits of detail that differs from show to book. In the books, Jeyne Westerling is alive and pregnant; Robb's Kingdom is literally still alive, and contained in Riverrun. Also, Blackfish is not at the Red Wedding in the books. OTOH in the show, Jeyne's counterpart and one of the most stupid and puzzling deviations from the books, "Talisa",

is butchered at the Red Wedding, and Blackfish
is present, and flees. Robb's kingdom is well and truly dead, and his motivations for an honorable death are also a bit more understandable (survivor's guilt).
Now, I'm not saying I think this was a flawlessly executed segment by any means, and I think some of its shortcomings stem from earlier slip-ups (as I outlined above), but overall I don't think it deserves the panning it has received. The Arya plotline conversely....yeah, not much good I can say on that one.

The director of that episode, Mark Mylod, has directed several of the lowest-rated episodes of the show on IMDB (which are still stupid-high since even meh episodes of GOT have a lot of great elements). Here's hoping the episode tonight brings the magic back somewhat.